Video decoding method using residual information in video coding system, and apparatus thereof

ABSTRACT

A video decoding method performed by a decoding apparatus according to the present document comprises the steps of: receiving a bit stream including residual information of a current block; deriving a specific number of the number of context encoding bins for context syntax elements for a current sub-block of the current block; decoding the context syntax elements for the current sub-block included in the residual information on the basis of the specific number; deriving transform coefficients for the current sub-block on the basis of the decoded context syntax elements; deriving residual samples for the current block on the basis of the transform coefficients; and generating a reconstructed picture on the basis of the residual samples.

BACKGROUND Technical Field

The present disclosure relates to an image coding technique and, moreparticularly, to an image decoding method for coding residualinformation including syntax elements for a transform coefficient of aresidual in an image coding system and an apparatus therefor.

Related Art

In recent years, the demand for high-resolution and high-quality images,such as high-definition (HD) and ultra-high-definition (UHD) images, hasbeen increasing in various fields. As image data has higher resolutionand higher quality, the amount of transmitted information or bitsincreases compared to conventional image data. Therefore, when imagedata is transmitted using a medium such as a conventional wired/wirelessbroadband line or image data is stored using an existing storage medium,transmission and storage costs are increased.

Accordingly, a high-efficiency image compression technique is requiredto effectively transmit or store and reproduce information onhigh-resolution and high-quality images.

SUMMARY

A technical aspect of the present disclosure is to provide a method andan apparatus for increasing image coding efficiency.

Another technical aspect of the present disclosure is to provide amethod and an apparatus for increasing residual coding efficiency.

Still another technical aspect of the present disclosure is to provide amethod and an apparatus for adjusting the number of context-coded binsfor a current subblock considering the total number of context-codedbins for context syntax elements when coding residual information.

According to an embodiment of the present disclosure, there is providedan image decoding method performed by a decoding apparatus. The methodincludes receiving a bitstream including residual information on acurrent block, deriving a specific number for a number of context-codedbins for context syntax elements for a current subblock of the currentblock, decoding the context syntax elements for the current subblockincluded in the residual information based on the specific number,deriving transform coefficients for the current subblock based on thedecoded context syntax elements, deriving residual samples for thecurrent block based on the transform coefficients; and generating areconstructed picture based on the residual samples, wherein, when atransform skip is applied to the current block, a significantcoefficient flag relating to whether a transform coefficient is anon-zero transform coefficient, a sign flag relating to a sign of thetransform coefficient, a first transform coefficient level flag relatingto whether a transform coefficient level is greater than a firstthreshold, a parity level flag relating to a parity of the transformcoefficient level of the transform coefficient, and a second transformcoefficient level flag relating to whether the transform coefficientlevel of the transform coefficient is greater than a second thresholdare decoded based on a context model until the specific number isreached.

According to another embodiment of the present disclosure, there isprovided a decoding apparatus for performing image decoding. Thedecoding apparatus includes an entropy decoder to receive a bitstreamincluding residual information on a current block, to derive a specificnumber for a number of context-coded bins for context syntax elementsfor a current subblock of the current block, to decode the contextsyntax elements for the current subblock included in the residualinformation based on the specific number, and to derive transformcoefficients for the current subblock based on the decoded contextsyntax elements, an inverse transformer to derive residual samples forthe current block based on the transform coefficients, and an adder togenerate a reconstructed picture based on the residual samples, wherein,when a transform skip is applied to the current block, a significantcoefficient flag relating to whether a transform coefficient is anon-zero transform coefficient, a sign flag relating to a sign of thetransform coefficient, a first transform coefficient level flag relatingto whether a transform coefficient level is greater than a firstthreshold, a parity level flag relating to a parity of the transformcoefficient level of the transform coefficient, and a second transformcoefficient level flag relating to whether the transform coefficientlevel of the transform coefficient is greater than a second thresholdare decoded based on a context model until the specific number isreached.

According to still another embodiment of the present disclosure, thereis provided an image encoding method performed by an encoding apparatus.The method may include deriving residual samples for a current block,deriving transform coefficients in a current subblock of the currentblock based on the residual samples, deriving a specific number for anumber of context-coded bins for context syntax elements for the currentsubblock, encoding the context syntax elements based on the specificnumber, and generating a bitstream including residual information on thecurrent block including the encoded context syntax elements, wherein,based on a transform skip being applied to the current block, asignificant coefficient flag relating to whether a transform coefficientis a non-zero transform coefficient, a sign flag relating to a sign ofthe transform coefficient, a first transform coefficient level flagrelating to whether a transform coefficient level is greater than afirst threshold, a parity level flag relating to a parity of thetransform coefficient level of the transform coefficient, and a secondtransform coefficient level flag relating to whether the transformcoefficient level of the transform coefficient is greater than a secondthreshold are decoded based on a context model until the specific numberis reached.

According to yet another embodiment of the present disclosure, there isprovided a video encoding apparatus. The encoding apparatus includes asubtractor to derive residual samples for a current block, a transformerto derive transform coefficients in a current subblock of the currentblock based on the residual samples, and an entropy encoder to derive aspecific number for a number of context-coded bins for context syntaxelements for the current subblock, to encode the context syntax elementsbased on the specific number, and to generate a bitstream includingresidual information on the current block including the encoded contextsyntax elements, wherein, based on a transform skip being applied to thecurrent block, a significant coefficient flag relating to whether atransform coefficient is a non-zero transform coefficient, a sign flagrelating to a sign of the transform coefficient, a first transformcoefficient level flag relating to whether a transform coefficient levelis greater than a first threshold, a parity level flag relating to aparity of the transform coefficient level of the transform coefficient,and a second transform coefficient level flag relating to whether thetransform coefficient level of the transform coefficient is greater thana second threshold are decoded based on a context model until thespecific number is reached.

According to still another embodiment of the present disclosure, theremay be provided a digital storage medium that stores image dataincluding encoded image information and a bitstream generated accordingto an image encoding method performed by an encoding apparatus.

According to yet another embodiment of the present disclosure, there maybe provided a digital storage medium that stores image data includingencoded image information and a bitstream to cause a decoding apparatusto perform the image decoding method.

According to the present disclosure, it is possible to increase overallimage/video compression efficiency.

According to the present disclosure, it is possible to increase theefficiency of residual coding.

According to the present disclosure, the total number of context-codedbins for context syntax elements for transform coefficients in a currentblock, which is included in residual information, may be limited to apredetermined specific number or less, thereby reducing data coded basedon context.

According to the present disclosure, the number of context-coded binsfor a current subblock may be adjusted considering the total number ofcontext-coded bins for context syntax elements rather than consideringcoding of each context syntax element, thus reducing the complexity ofresidual coding and improving overall coding efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example of a video/image codingsystem to which embodiments of the present disclosure are applicable.

FIG. 2 schematically illustrates the configuration of a video/imageencoding apparatus to which embodiments of the present disclosure areapplicable.

FIG. 3 schematically illustrates the configuration of a video/imagedecoding apparatus to which embodiments of the present disclosure areapplicable.

FIG. 4 illustrates context-adaptive binary arithmetic coding (CABAC) forencoding a syntax element.

FIG. 5 illustrates an example of transform coefficients in a 4×4 block.

FIG. 6 illustrates a decoding apparatus for performing a proposed methodfor transmitting a residual signal in a pixel domain.

FIG. 7A and FIG. 7B illustrate an embodiment of determining whether toparse a transform skip flag based on the number of samples of a currentblock and a decoding apparatus performing the embodiment.

FIG. 8 illustrates residual coefficients of a current block to which arearrangement method of 180-degree rotation is applied.

FIG. 9 illustrates residual coefficients of a current block to which arearrangement method of mirroring is applied.

FIG. 10 illustrates residual coefficients of a current block to which arearrangement method of flipping is applied.

FIG. 11 illustrates residual coefficients of a current block to which anembodiment of dividing layers based on the distance to a referencesample and performing rearrangement at positions according to an inverseraster order is applied.

FIG. 12 illustrates residual coefficients of a current block to which anembodiment of dividing layers based on the distance to a referencesample and performing rearrangement at positions according to a diagonalscan order is applied.

FIG. 13 illustrates residual coefficients of a current block to whichthe foregoing embodiment of dividing layers based on the distance to aspecific reference sample and performing rearrangement at positionsaccording to a diagonal scan order is applied.

FIG. 14A and FIG. 14B illustrate an embodiment of determining whether toapply a rearrangement method based on a transform skip flag for acurrent block and an encoding apparatus and a decoding apparatusperforming the embodiment.

FIG. 15 illustrates an example of determining a method of codingresidual information based on a transform skip flag.

FIG. 16 illustrates an example of determining a method of codingresidual information based on unified transform type information.

FIG. 17 schematically illustrates an image encoding method by anencoding apparatus according to the present disclosure.

FIG. 18 schematically illustrates an encoding apparatus that performs animage encoding method according to the present disclosure.

FIG. 19 schematically illustrates an image decoding method by a decodingapparatus according to the present disclosure.

FIG. 20 schematically illustrates a decoding apparatus that performs animage decoding method according to the present disclosure.

FIG. 21 illustrates the structure of a content streaming system to whichthe embodiments of the present disclosure are applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

While the present disclosure may be susceptible to various modificationsand include various embodiments, specific embodiments thereof have beenshown in the drawings by way of example and will now be described indetail. However, this is not intended to limit embodiments of thepresent disclosure to the specific embodiments disclosed herein. Theterminology used herein is for the purpose of describing specificembodiments only, and is not intended to limit technical idea of thepresent document. The singular forms may include the plural forms unlessthe context clearly indicates otherwise. The terms such as “include” and“have” are intended to indicate that features, numbers, steps,operations, elements, components, or combinations thereof used in thefollowing description exist, and thus should not be understood as thatthe possibility of existence or addition of one or more differentfeatures, numbers, steps, operations, elements, components, orcombinations thereof is excluded in advance.

Each component on the drawings described herein is illustratedindependently for convenience of description as to characteristicfunctions different from each other, and however, it is not meant thateach component is realized by a separate hardware or software. Forexample, any two or more of these components may be combined to form asingle component, and any single component may be divided into pluralcomponents. The embodiments in which components are combined and/ordivided will belong to the scope of the patent right of the presentdocument as long as they do not depart from the essence of the presentdocument.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Inaddition, like reference numerals are used to indicate like elementsthroughout the drawings, and redundant descriptions of like elementswill be omitted.

FIG. 1 schematically illustrates an example of a video/image codingsystem to which embodiments of the present disclosure are applicable.

Referring to FIG. 1, a video/image coding system may include a sourcedevice and a reception device. The source device may transmit encodedvideo/image information or data to the reception device through adigital storage medium or network in the form of a file or streaming.

The source device may include a video source, an encoding apparatus, anda transmitter. The receiving device may include a receiver, a decodingapparatus, and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display, and the display may beconfigured as a separate device or an external component.

The video source may acquire video/image through a process of capturing,synthesizing, or generating the video/image. The video source mayinclude a video/image capture device and/or a video/image generatingdevice. The video/image capture device may include, for example, one ormore cameras, video/image archives including previously capturedvideo/images, and the like. The video/image generating device mayinclude, for example, computers, tablets and smartphones, and may(electronically) generate video/images. For example, a virtualvideo/image may be generated through a computer or the like. In thiscase, the video/image capturing process may be replaced by a process ofgenerating related data.

The encoding apparatus may encode input video/image. The encodingapparatus may perform a series of procedures such as prediction,transform, and quantization for compaction and coding efficiency. Theencoded data (encoded video/image information) may be output in the formof a bitstream.

The transmitter may transmit the encoded image/image information or dataoutput in the form of a bitstream to the receiver of the receivingdevice through a digital storage medium or a network in the form of afile or streaming The digital storage medium may include various storagemediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. Thetransmitter may include an element for generating a media file through apredetermined file format and may include an element for transmissionthrough a broadcast/communication network. The receiver mayreceive/extract the bitstream and transmit the received bitstream to thedecoding apparatus.

The decoding apparatus may decode the video/image by performing a seriesof procedures such as dequantization, inverse transform, and predictioncorresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display.

This document relates to video/image coding. For example, amethod/embodiment disclosed in this document may be applied to a methoddisclosed in the versatile video coding (VVC) standard, the essentialvideo coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the 2ndgeneration of audio video coding standard (AVS2) or the next generationvideo/image coding standard (e.g., H.267, H.268, or the like).

This document suggests various embodiments of video/image coding, andthe above embodiments may also be performed in combination with eachother unless otherwise specified.

In this document, a video may refer to a series of images over time. Apicture generally refers to the unit representing one image at aparticular time frame, and a slice/tile refers to the unit constitutinga part of the picture in terms of coding. A slice/tile may include oneor more coding tree units (CTUs). One picture may consist of one or moreslices/tiles. One picture may consist of one or more tile groups. Onetile group may include one or more tiles. A brick may represent arectangular region of CTU rows within a tile in a picture (a brick mayrepresent a rectangular region of CTU rows within a tile in a picture).A tile may be partitioned into a multiple bricks, each of which may beconstructed with one or more CTU rows within the tile (A tile may bepartitioned into multiple bricks, each of which consisting of one ormore CTU rows within the tile). A tile that is not partitioned intomultiple bricks may also be referred to as a brick. A brick scan mayrepresent a specific sequential ordering of CTUs partitioning a picture,wherein the CTUs may be ordered in a CTU raster scan within a brick, andbricks within a tile may be ordered consecutively in a raster scan ofthe bricks of the tile, and tiles in a picture may be orderedconsecutively in a raster scan of the tiles of the picture (A brick scanis a specific sequential ordering of CTUs partitioning a picture inwhich the CTUs are ordered consecutively in CTU raster scan in a brick,bricks within a tile are ordered consecutively in a raster scan of thebricks of the tile, and tiles in a picture are ordered consecutively ina raster scan of the tiles of the picture). A tile is a particular tilecolumn and a rectangular region of CTUs within a particular tile column(A tile is a rectangular region of CTUs within a particular tile columnand a particular tile row in a picture). The tile column is arectangular region of CTUs, which has a height equal to the height ofthe picture and a width that may be specified by syntax elements in thepicture parameter set (The tile column is a rectangular region of CTUshaving a height equal to the height of the picture and a width specifiedby syntax elements in the picture parameter set). The tile row is arectangular region of CTUs, which has a width specified by syntaxelements in the picture parameter set and a height that may be equal tothe height of the picture (The tile row is a rectangular region of CTUshaving a height specified by syntax elements in the picture parameterset and a width equal to the width of the picture). A tile scan mayrepresent a specific sequential ordering of CTUs partitioning a picture,and the CTUs may be ordered consecutively in a CTU raster scan in atile, and tiles in a picture may be ordered consecutively in a rasterscan of the tiles of the picture (A tile scan is a specific sequentialordering of CTUs partitioning a picture in which the CTUs are orderedconsecutively in CTU raster scan in a tile whereas tiles in a pictureare ordered consecutively in a raster scan of the tiles of the picture).A slice may include an integer number of bricks of a picture, and theinteger number of bricks may be included in a single NAL unit (A sliceincludes an integer number of bricks of a picture that may beexclusively contained in a single NAL unit). A slice may be constructedwith multiple complete tiles, or may be a consecutive sequence ofcomplete bricks of one tile (A slice may consists of either a number ofcomplete tiles or only a consecutive sequence of complete bricks of onetile). In this document, a tile group and a slice may be used in placeof each other. For example, in this document, a tile group/tile groupheader may be referred to as a slice/slice header.

A pixel or a pa may mean a smallest unit constituting one picture (orimage). Also, ‘sample’ may be used as a term corresponding to a pixel. Asample may generally represent a pixel or a value of a pixel, and mayrepresent only a pixel/pixel value of a luma component or only apixel/pixel value of a chroma component.

A unit may represent a basic unit of image processing. The unit mayinclude at least one of a specific region of the picture and informationrelated to the region. One unit may include one luma block and twochroma (e.g., cb and cr) blocks. The unit may be used interchangeablywith terms such as block or area in some cases. In a general case, anM×N block may include samples (or sample arrays) or a set (or array) oftransform coefficients of M columns and N rows.

In this document, the symbol“/” and “,” should be interpreted as“and/or.” For example, the expression “A/B” is interpreted as “A and/orB”, and the expression “A, B” is interpreted as “A and/or B.”Additionally, the expression “A/B/C” means “at least one of A, B, and/orC.” Further, the expression “A, B, C” also means “at least one of A, B,and/or C.” (In this document, the term “/” and “,” should be interpretedto indicate “and/or.” For instance, the expression “A/B” may mean “Aand/or B.” Further, “A, B” may mean “A and/or B.” Further, “A/B/C” maymean “at least one of A, B, and/or C.” Also, “A/B/C” may mean “at leastone of A, B, and/or C.”)

Additionally, in the present document, the term “or” should beinterpreted as “and/or.” For example, the expression “A or B” maymean 1) only “A”, 2) only “B”, and/or 3) “both A and B.” In other words,the term “or” in the present document may mean “additionally oralternatively.” (Further, in the document, the term “or” should beinterpreted to indicate “and/or.” For instance, the expression “A or B”may include 1) only A, 2) only B, and/or 3) both A and B. In otherwords, the term “or” in this document should be interpreted to indicate“additionally or alternatively.”)

FIG. 2 schematically illustrates the configuration of a video/imageencoding apparatus to which embodiments of the present disclosure areapplicable. Hereinafter, a video encoding apparatus may include an imageencoding apparatus.

Referring to FIG. 2, the encoding apparatus 200 may include and beconfigured with an image partitioner 210, a predictor 220, a residualprocessor 230, an entropy encoder 240, an adder 250, a filter 260, and amemory 270. The predictor 220 may include an inter predictor 221 and anintra predictor 222. The residual processor 230 may include atransformer 232, a quantizer 233, a dequantizer 234, and an inversetransformer 235. The residual processor 230 may further include asubtractor 231. The adder 250 may be called a reconstructor orreconstructed block generator. The image partitioner 210, the predictor220, the residual processor 230, the entropy encoder 240, the adder 250,and the filter 260, which have been described above, may be configuredby one or more hardware components (e.g., encoder chipsets orprocessors) according to an embodiment. In addition, the memory 270 mayinclude a decoded picture buffer (DPB), and may also be configured by adigital storage medium. The hardware component may further include thememory 270 as an internal/external component.

The image partitioner 210 may split an input image (or, picture, frame)input to the encoding apparatus 200 into one or more processing units.As an example, the processing unit may be called a coding unit (CU). Inthis case, the coding unit may be recursively split according to aQuad-tree binary-tree ternary-tree (QTBTTT) structure from a coding treeunit (CTU) or the largest coding unit (LCU). For example, one codingunit may be split into a plurality of coding units of a deeper depthbased on a quad-tree structure, a binary-tree structure, and/or aternary-tree structure. In this case, for example, the quad-treestructure is first applied and the binary-tree structure and/or theternary-tree structure may be later applied. Alternatively, thebinary-tree structure may also be first applied. A coding procedureaccording to the present disclosure may be performed based on a finalcoding unit which is not split any more. In this case, based on codingefficiency according to image characteristics or the like, the maximumcoding unit may be directly used as the final coding unit, or asnecessary, the coding unit may be recursively split into coding units ofa deeper depth, such that a coding unit having an optimal size may beused as the final coding unit. Here, the coding procedure may include aprocedure such as prediction, transform, and reconstruction to bedescribed later. As another example, the processing unit may furtherinclude a prediction unit (PU) or a transform unit (TU). In this case,each of the prediction unit and the transform unit may be split orpartitioned from the aforementioned final coding unit. The predictionunit may be a unit of sample prediction, and the transform unit may be aunit for inducing a transform coefficient and/or a unit for inducing aresidual signal from the transform coefficient.

The unit may be interchangeably used with the term such as a block or anarea in some cases. Generally, an M×N block may represent samplescomposed of M columns and N rows or a group of transform coefficients.The sample may generally represent a pixel or a value of the pixel, andmay also represent only the pixel/pixel value of a luma component, andalso represent only the pixel/pixel value of a chroma component. Thesample may be used as the term corresponding to a pixel or a pelconfiguring one picture (or image).

The encoding apparatus 200 may generate a residual signal (residualblock, residual sample array) by subtracting a predicted signal(predicted block, prediction sample array) output from the interpredictor 221 or the intra predictor 222 from the input image signal(original block, original sample array), and the generated residualsignal is transmitted to the transformer 232. In this case, asillustrated, the unit for subtracting the predicted signal (predictedblock, prediction sample array) from the input image signal (originalblock, original sample array) within an encoder 200 may be called thesubtractor 231. The predictor may perform prediction for a block to beprocessed (hereinafter, referred to as a current block), and generate apredicted block including prediction samples of the current block. Thepredictor may determine whether intra prediction is applied or interprediction is applied in units of the current block or the CU. Thepredictor may generate various information about prediction, such asprediction mode information, to transfer the generated information tothe entropy encoder 240 as described later in the description of eachprediction mode. The information about prediction may be encoded by theentropy encoder 240 to be output in a form of the bitstream.

The intra predictor 222 may predict a current block with reference tosamples within a current picture. The referenced samples may be locatedneighboring to the current block, or may also be located away from thecurrent block according to the prediction mode. The prediction modes inthe intra prediction may include a plurality of non-directional modesand a plurality of directional modes. The non-directional mode mayinclude, for example, a DC mode or a planar mode. The directional modemay include, for example, 33 directional prediction modes or 65directional prediction modes according to the fine degree of theprediction direction. However, this is illustrative and the directionalprediction modes which are more or less than the above number may beused according to the setting. The intra predictor 222 may alsodetermine the prediction mode applied to the current block using theprediction mode applied to the neighboring block.

The inter predictor 221 may induce a predicted block of the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. At this time, in order to decreasethe amount of motion information transmitted in the inter predictionmode, the motion information may be predicted in units of a block, asub-block, or a sample based on the correlation of the motioninformation between the neighboring block and the current block. Themotion information may include a motion vector and a reference pictureindex. The motion information may further include inter predictiondirection (L0 prediction, L1 prediction, Bi prediction, or the like)information. In the case of the inter prediction, the neighboring blockmay include a spatial neighboring block existing within the currentpicture and a temporal neighboring block existing in the referencepicture. The reference picture including the reference block and thereference picture including the temporal neighboring block may also bethe same as each other, and may also be different from each other. Thetemporal neighboring block may be called the name such as a collocatedreference block, a collocated CU (colCU), or the like, and the referencepicture including the temporal neighboring block may also be called acollocated picture (colPic). For example, the inter predictor 221 mayconfigure a motion information candidate list based on the neighboringblocks, and generate information indicating what candidate is used toderive the motion vector and/or the reference picture index of thecurrent block. The inter prediction may be performed based on variousprediction modes, and for example, in the case of a skip mode and amerge mode, the inter predictor 221 may use the motion information ofthe neighboring block as the motion information of the current block. Inthe case of the skip mode, the residual signal may not be transmittedunlike the merge mode. A motion vector prediction (MVP) mode mayindicate the motion vector of the current block by using the motionvector of the neighboring block as a motion vector predictor, andsignaling a motion vector difference.

The predictor 200 may generate a predicted signal based on variousprediction methods to be described later. For example, the predictor maynot only apply the intra prediction or the inter prediction forpredicting one block, but also simultaneously apply the intra predictionand the inter prediction. This may be called a combined inter and intraprediction (CIIP). Further, the predictor may be based on an intra blockcopy (IBC) prediction mode, or a palette mode in order to performprediction on a block. The IBC prediction mode or palette mode may beused for content image/video coding of a game or the like, such asscreen content coding (SCC). The IBC basically performs prediction in acurrent picture, but it may be performed similarly to inter predictionin that it derives a reference block in a current picture. That is, theIBC may use at least one of inter prediction techniques described in thepresent document. The palette mode may be regarded as an example ofintra coding or intra prediction. When the palette mode is applied, asample value in a picture may be signaled based on information on apalette index and a palette table.

The predicted signal generated through the predictor (including theinter predictor 221 and/or the intra predictor 222) may be used togenerate a reconstructed signal or used to generate a residual signal.The transformer 232 may generate transform coefficients by applying thetransform technique to the residual signal. For example, the transformtechnique may include at least one of a discrete cosine transform (DCT),a discrete sine transform (DST), a Karhunen-Loève transform (KLT), agraph-based transform (GBT), or a conditionally non-linear transform(CNT). Here, when the relationship information between pixels isillustrated as a graph, the GBT means the transform obtained from thegraph. The CNT means the transform which is acquired based on apredicted signal generated by using all previously reconstructed pixels.In addition, the transform process may also be applied to a pixel blockhaving the same size of the square, and may also be applied to the blockhaving a variable size rather than the square.

The quantizer 233 may quantize the transform coefficients to transmitthe quantized transform coefficients to the entropy encoder 240, and theentropy encoder 240 may encode the quantized signal (information aboutthe quantized transform coefficients) to the encoded quantized signal tothe bitstream. The information about the quantized transformcoefficients may be called residual information. The quantizer 233 mayrearrange the quantized transform coefficients having a block form in aone-dimensional vector form based on a coefficient scan order, and alsogenerate the information about the quantized transform coefficientsbased on the quantized transform coefficients of the one dimensionalvector form. The entropy encoder 240 may perform various encodingmethods, for example, such as an exponential Golomb coding, acontext-adaptive variable length coding (CAVLC), and a context-adaptivebinary arithmetic coding (CABAC). The entropy encoder 240 may alsoencode information (e.g., values of syntax elements and the like)necessary for reconstructing video/image other than the quantizedtransform coefficients together or separately. The encoded information(e.g., encoded video/image information) may be transmitted or stored inunits of network abstraction layer (NAL) unit in a form of thebitstream. The video/image information may further include informationabout various parameter sets such as an adaptation parameter set (APS),a picture parameter set (PPS), a sequence parameter set (SPS), or avideo parameter set (VPS). In addition, the video/image information mayfurther include general constraint information. The signaled/transmittedinformation and/or syntax elements to be described later in thisdocument may be encoded through the aforementioned encoding procedureand thus included in the bitstream. The bitstream may be transmittedthrough a network, or stored in a digital storage medium. Here, thenetwork may include a broadcasting network and/or a communicationnetwork, or the like, and the digital storage medium may include variousstorage media such as USB, SD, CD, DVD, Blue-ray, HDD, and SSD. Atransmitter (not illustrated) for transmitting the signal output fromthe entropy encoder 240 and/or a storage (not illustrated) for storingthe signal may be configured as the internal/external elements of theencoding apparatus 200, or the transmitter may also be included in theentropy encoder 240.

The quantized transform coefficients output from the quantizer 233 maybe used to generate a predicted signal. For example, the dequantizer 234and the inverse transformer 235 apply dequantization and inversetransform to the quantized transform coefficients, such that theresidual signal (residual block or residual samples) may bereconstructed. The adder 250 adds the reconstructed residual signal tothe predicted signal output from the inter predictor 221 or the intrapredictor 222, such that the reconstructed signal (reconstructedpicture, reconstructed block, reconstructed sample array) may begenerated. As in the case where the skip mode is applied, if there is noresidual for the block to be processed, the predicted block may be usedas the reconstructed block. The adder 250 may be called a reconstructoror a reconstructed block generator. The generated reconstructed signalmay be used for the intra prediction of the next block to be processedwithin the current picture, and as described later, also used for theinter prediction of the next picture through filtering.

Meanwhile, a luma mapping with chroma scaling (LMCS) may also be appliedin a picture encoding and/or reconstruction process.

The filter 260 may apply filtering to the reconstructed signal, therebyimproving subjective/objective image qualities. For example, the filter260 may apply various filtering methods to the reconstructed picture togenerate a modified reconstructed picture, and store the modifiedreconstructed picture in the memory 270, specifically, the DPB of thememory 270. Various filtering methods may include, for example, adeblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like. The filter 260 may generate variousfiltering-related information to transfer the generated information tothe entropy encoder 240, as described later in the description of eachfiltering method. The filtering-related information may be encoded bythe entropy encoder 240 to be output in a form of the bitstream.

The modified reconstructed picture transmitted to the memory 270 may beused as the reference picture in the inter predictor 221. If the interprediction is applied by the inter predictor, the encoding apparatus mayavoid the prediction mismatch between the encoding apparatus 200 and thedecoding apparatus 300, and also improve coding efficiency.

The DPB of the memory 270 may store the modified reconstructed pictureto be used as the reference picture in the inter predictor 221. Thememory 270 may store motion information of the block in which the motioninformation within the current picture is derived (or encoded) and/ormotion information of the blocks within the previously reconstructedpicture. The stored motion information may be transferred to the interpredictor 221 to be utilized as motion information of the spatialneighboring block or motion information of the temporal neighboringblock. The memory 270 may store the reconstructed samples of thereconstructed blocks within the current picture, and transfer thereconstructed samples to the intra predictor 222.

FIG. 3 schematically illustrates the configuration of a video/imagedecoding apparatus to which embodiments of the present disclosure areapplicable.

Referring to FIG. 3, the decoding apparatus 300 may include andconfigured with an entropy decoder 310, a residual processor 320, apredictor 330, an adder 340, a filter 350, and a memory 360. Thepredictor 330 may include an inter predictor 331 and an intra predictor332. The residual processor 320 may include a dequantizer 321 and aninverse transformer 322. The entropy decoder 310, the residual processor320, the predictor 330, the adder 340, and the filter 350, which havebeen described above, may be configured by one or more hardwarecomponents (e.g., decoder chipsets or processors) according to anembodiment. Further, the memory 360 may include a decoded picture buffer(DPB), and may be configured by a digital storage medium. The hardwarecomponent may further include the memory 360 as an internal/externalcomponent.

When the bitstream including the video/image information is input, thedecoding apparatus 300 may reconstruct the image in response to aprocess in which the video/image information is processed in theencoding apparatus illustrated in FIG. 2. For example, the decodingapparatus 300 may derive the units/blocks based on block split-relatedinformation acquired from the bitstream. The decoding apparatus 300 mayperform decoding using the processing unit applied to the encodingapparatus. Therefore, the processing unit for the decoding may be, forexample, a coding unit, and the coding unit may be split according tothe quad-tree structure, the binary-tree structure, and/or theternary-tree structure from the coding tree unit or the maximum codingunit. One or more transform units may be derived from the coding unit.In addition, the reconstructed image signal decoded and output throughthe decoding apparatus 300 may be reproduced through a reproducingapparatus.

The decoding apparatus 300 may receive the signal output from theencoding apparatus illustrated in FIG. 2 in a form of the bitstream, andthe received signal may be decoded through the entropy decoder 310. Forexample, the entropy decoder 310 may derive information (e.g.,video/image information) necessary for the image reconstruction (orpicture reconstruction) by parsing the bitstream. The video/imageinformation may further include information about various parameter setssuch as an adaptation parameter set (APS), a picture parameter set(PPS), a sequence parameter set (SPS), and a video parameter set (VPS).In addition, the video/image information may further include generalconstraint information. The decoding apparatus may decode the picturefurther based on the information about the parameter set and/or thegeneral constraint information. The signaled/received information and/orsyntax elements to be described later in this document may be decodedthrough the decoding procedure and acquired from the bitstream. Forexample, the entropy decoder 310 may decode information within thebitstream based on a coding method such as an exponential Golomb coding,a CAVLC, or a CABAC, and output a value of the syntax element necessaryfor the image reconstruction, and the quantized values of theresidual-related transform coefficient. More specifically, the CABACentropy decoding method may receive a bin corresponding to each syntaxelement from the bitstream, determine a context model using syntaxelement information to be decoded and decoding information of theneighboring block and the block to be decoded or information of thesymbol/bin decoded in the previous stage, and generate a symbolcorresponding to a value of each syntax element by predicting theprobability of generation of the bin according to the determined contextmodel to perform the arithmetic decoding of the bin. At this time, theCABAC entropy decoding method may determine the context model and thenupdate the context model using the information of the decoded symbol/binfor a context model of a next symbol/bin. The information aboutprediction among the information decoded by the entropy decoder 310 maybe provided to the predictor (the inter predictor 332 and the intrapredictor 331), and a residual value at which the entropy decoding isperformed by the entropy decoder 310, that is, the quantized transformcoefficients and the related parameter information may be input to theresidual processor 320. The residual processor 320 may derive a residualsignal (residual block, residual samples, residual sample array). Inaddition, the information about filtering among the information decodedby the entropy decoder 310 may be provided to the filter 350. Meanwhile,a receiver (not illustrated) for receiving the signal output from theencoding apparatus may be further configured as the internal/externalelement of the decoding apparatus 300, or the receiver may also be acomponent of the entropy decoder 310. Meanwhile, the decoding apparatusaccording to this document may be called a video/image/picture decodingapparatus, and the decoding apparatus may also be classified into aninformation decoder (video/image/picture information decoder) and asample decoder (video/image/picture sample decoder). The informationdecoder may include the entropy decoder 310, and the sample decoder mayinclude at least one of the dequantizer 321, the inverse transformer322, the adder 340, the filter 350, the memory 360, the inter predictor332, and the intra predictor 331.

The dequantizer 321 may dequantize the quantized transform coefficientsto output the transform coefficients. The dequantizer 321 may rearrangethe quantized transform coefficients in a two-dimensional block form. Inthis case, the rearrangement may be performed based on a coefficientscan order performed by the encoding apparatus. The dequantizer 321 mayperform dequantization for the quantized transform coefficients using aquantization parameter (e.g., quantization step size information), andacquire the transform coefficients.

The inverse transformer 322 inversely transforms the transformcoefficients to acquire the residual signal (residual block, residualsample array).

The predictor 330 may perform the prediction of the current block, andgenerate a predicted block including the prediction samples of thecurrent block. The predictor may determine whether the intra predictionis applied or the inter prediction is applied to the current block basedon the information about prediction output from the entropy decoder 310,and determine a specific intra/inter prediction mode.

The predictor may generate the predicted signal based on variousprediction methods to be described later. For example, the predictor maynot only apply the intra prediction or the inter prediction for theprediction of one block, but also apply the intra prediction and theinter prediction at the same time. This may be called a combined interand intra prediction (CIIP). Further, the predictor may be based on anintra block copy (IBC) prediction mode, or a palette mode in order toperform prediction on a block. The IBC prediction mode or palette modemay be used for content image/video coding of a game or the like, suchas screen content coding (SCC). The IBC basically performs prediction ina current picture, but it may be performed similarly to inter predictionin that it derives a reference block in a current picture. That is, theIBC may use at least one of inter prediction techniques described in thepresent document. The palette mode may be regarded as an example ofintra coding or intra prediction. When the palette mode is applied,information on a palette table and a palette index may be included inthe video/image information and signaled.

The intra predictor 331 may predict the current block with reference tothe samples within the current picture. The referenced samples may belocated neighboring to the current block according to the predictionmode, or may also be located away from the current block. The predictionmodes in the intra prediction may include a plurality of non-directionalmodes and a plurality of directional modes. The intra predictor 331 mayalso determine the prediction mode applied to the current block usingthe prediction mode applied to the neighboring block.

The inter predictor 332 may induce the predicted block of the currentblock based on the reference block (reference sample array) specified bythe motion vector on the reference picture. At this time, in order todecrease the amount of the motion information transmitted in the interprediction mode, the motion information may be predicted in units of ablock, a sub-block, or a sample based on the correlation of the motioninformation between the neighboring block and the current block. Themotion information may include a motion vector and a reference pictureindex. The motion information may further include inter predictiondirection (L0 prediction, L1 prediction, Bi prediction, or the like)information. In the case of the inter prediction, the neighboring blockmay include a spatial neighboring block existing within the currentpicture and a temporal neighboring block existing in the referencepicture. For example, the inter predictor 332 may configure a motioninformation candidate list based on the neighboring blocks, and derivethe motion vector and/or the reference picture index of the currentblock based on received candidate selection information. The interprediction may be performed based on various prediction modes, and theinformation about the prediction may include information indicating themode of the inter prediction of the current block.

The adder 340 may add the acquired residual signal to the predictedsignal (predicted block, prediction sample array) output from thepredictor (including the inter predictor 332 and/or the intra predictor331) to generate the reconstructed signal (reconstructed picture,reconstructed block, reconstructed sample array). As in the case wherethe skip mode is applied, if there is no residual for the block to beprocessed, the predicted block may be used as the reconstructed block.

The adder 340 may be called a reconstructor or a reconstructed blockgenerator. The generated reconstructed signal may be used for the intraprediction of a next block to be processed within the current picture,and as described later, may also be output through filtering or may alsobe used for the inter prediction of a next picture.

Meanwhile, a luma mapping with chroma scaling (LMCS) may also be appliedin the picture decoding process.

The filter 350 may apply filtering to the reconstructed signal, therebyimproving the subjective/objective image qualities. For example, thefilter 350 may apply various filtering methods to the reconstructedpicture to generate a modified reconstructed picture, and transmit themodified reconstructed picture to the memory 360, specifically, the DPBof the memory 360. Various filtering methods may include, for example, adeblocking filtering, a sample adaptive offset, an adaptive loop filter,a bidirectional filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 360may be used as the reference picture in the inter predictor 332. Thememory 360 may store motion information of the block in which the motioninformation within the current picture is derived (decoded) and/ormotion information of the blocks within the previously reconstructedpicture. The stored motion information may be transferred to the interpredictor 260 to be utilized as motion information of the spatialneighboring block or motion information of the temporal neighboringblock. The memory 360 may store the reconstructed samples of thereconstructed blocks within the current picture, and transfer the storedreconstructed samples to the intra predictor 331.

In the present specification, the exemplary embodiments described in thefilter 260, the inter predictor 221, and the intra predictor 222 of theencoding apparatus 200 may be applied equally to or to correspond to thefilter 350, the inter predictor 332, and the intra predictor 331 of thedecoding apparatus 300, respectively.

As described above, the encoding apparatus may perform various encodingmethods, such as exponential Golomb coding, context-adaptive variablelength coding (CAVLC), and context-adaptive binary arithmetic coding(CABAC). In addition, the decoding apparatus may decode information in abitstream based on a coding method, such as exponential Golomb coding,CAVLC, or CABAC, and may output the value of a syntax element necessaryfor image reconstruction and quantized values of a transform coefficientregarding a residual.

For example, the foregoing coding methods may be performed as describedbelow.

FIG. 4 illustrates context-adaptive binary arithmetic coding (CABAC) forencoding a syntax element. For example, in an encoding process of CABAC,when an input signal is a syntax element rather than a binary value, anencoding apparatus may convert the input signal into a binary value bybinarizing the value of the input signal. When the input signal isalready a binary value (i.e., the value of the input signal is a binaryvalue), the input signal may be bypassed without binarization. Here,each binary 0 or 1 forming the binary value may be referred to as a bin.For example, when a binary string resulting from the binarization is110, each of 1, 1, and 0 is called one bin. The bin(s) for one syntaxelement may indicate the value of the syntax element.

The binarized bins of the syntax element may be input to a regularcoding engine or a bypass coding engine. The regular coding engine ofthe encoding apparatus may assign a context model that reflects aprobability value for the bins and may encode the bins based on theassigned context model. The regular coding engine of the encodingapparatus may encode on each bin and may then update the context modelfor the bin. These encoded bins may be referred to as context-codedbins.

When the binarized bins of the syntax element are input to the bypasscoding engine, the bins may be coded as follows. For example, the bypasscoding engine of the encoding apparatus omits a procedure of estimatinga probability for the input bins and a procedure of updating aprobability model applied to the bins after encoding. When bypassencoding is applied, the encoding apparatus may encode the input bits byapplying a uniform probability distribution instead of assigning acontext model, thus increasing encoding speed. These coded bins may bereferred to as bypass bins.

Entropy decoding may be performed by the same process as entropyencoding described above in reverse order.

For example, when the syntax element is decoded based on a contextmodel, the decoding apparatus may receive a bin corresponding to thesyntax element through the bitstream, may determine the context modelusing the syntax element and decoding information on a block to bedecoded or a neighboring block or information on a symbol/bin decoded ina previous step, and may derive the value of the syntax element bypredicting the probability of the received bin occurring and performingarithmetic decoding of the bin according to the determined contextmodel. Subsequently, a context model for a bin to be subsequentlydecoded may be updated to the determined context model.

Further, for example, when the syntax element is subjected to bypassdecoding, the decoding apparatus may receive the bin corresponding tothe syntax element through the bitstream and may decode the input bin byapplying a uniform probability distribution. In this case, the decodingapparatus may omit the procedure of deriving the context model for thesyntax element and the procedure of updating the context model appliedto the bin after decoding.

As described above, residual samples may be derived as quantizedtransform coefficients through transform and quantization processes. Thequantized transform coefficients may also be referred to as transformcoefficients. In this case, the transform coefficients within a blockmay be signaled in the form of residual information. The residualinformation may include a residual coding syntax. That is, the encodingapparatus may construct the residual coding syntax with the residualinformation, may encode the residual coding syntax, and may outputresidual coding syntax in the form of a bitstream, and the decodingapparatus may decode the residual coding syntax from the bitstream andmay derive residual (quantized) transform coefficients. As describedbelow, the residual coding syntax may include syntax elements indicatingwhether a transform is applied to the block, the position of the lastsignificant transform coefficient in the block, whether there is asignificant transform coefficient in a subblock, the size/code of asignificant transform coefficient, and the like.

For example, the (quantized) transform coefficients (i.e., the residualinformation) may be encoded and/or decoded based on syntax elements,such as transform_skip_flag, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag,par_level_flag, abs_level_gt1_flag, abs_level_gt3_flag, abs_remainder,coeff_sign_flag, and mts_idx. The syntax elements related to residualdata encoding/decoding may be illustrated in the following table.

TABLE 1 Descriptor residual_coding( x0, y0, log2TbWidth, log2TbHeight,cIdx ) {  if( transform_skip_enabled_flag && ( cIdx ! = 0 ||tu_mts_flag[ x0 ][ y0 ] = = 0 ) &&   ( log2TbWidth <= 2 ) && (log2TbHeight <= 2 ) )   transform_skip_flag[ x0 ][ y0 ][ cIdx ] ae(v) last_sig_coeff_x_prefix ae(v)  last_sig_coeff_y_prefix ae(v)  if(last_sig_coeff_x_prefix > 3 )   last_sig_coeff_x_suffix ae(v)  if(last_sig_coeff_y_prefix > 3 )   last_sig_coeff_y_suffix ae(v) log2SbSize = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2 ) numSbCoeff = 1 << ( log2SbSize << 1 )  lastScanPos = numSbCoeff lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − 2 * log2SbSize ) )− 1  do {   if( lastScanPos = = 0 ) {    lastScanPos = numSbCoeff   lastSubBlock− −   }   lastScanPos   xS = DiagScanOrder[ log2TbWidth −log2SbSize ][ log2TbHeight − log2SbSize ]          [ lastSubBlock ][ 0 ]  yS = DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight −log2SbSize ]          [ lastSubBlock ][ 1 ]   xC = ( xS << log2SbSize) +      DiagScanOrder[ log2SbSize ][ log2SbSize ][ lastScanPos ][ 0 ]  yC = ( yS << log2SbSize ) +      DiagScanOrder[ log2SbSize ][log2SbSize ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX) ( yC != LastSignificantCoeffY ) )  numSigCoeff = 0  QState = 0  for( i= lastSubBlock; i >= 0; i− − ) {   startQStateSb = QState   xS =DiagScanOrder[ log2TbWidth log2SbSize ][ log2TbHeight log2SbSize ]         [ lastSubBlock ][ 0 ]   yS = DiagScanOrder[ log2TbWidth −log2SbSize ][ log2TbHeight − log2SbSize ]          [ lastSubBlock ][ 1 ]  inferSbDcSigCoeffFlag = 0      if( ( i < lastSubBlock ) && ( i > 0 ) ){       coded_sub_block_flag[ xS ][ yS ] ae(v)      inferSbDcSigCoeffFlag = 1      }      firstSigScanPosSb =numSbCoeff      lastSigScanPosSb = −1      remBinsPass1 = ( log2SbSize <2 ? 6 : 28 )      remBinsPass2 = ( log2SbSize < 2 ? 2 : 4 )     firstPosMode0 = ( i = = lastSubBlock ? lastScanPos 1 : numSbCoeff 1)      firstPosMode1 = −1      firstPosMode2 = −1      for( n = ( i = =firstPosMode0; n >= 0 && remBinsPass1 >= 3; n− − ) {       xC = ( xS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]      yC = ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 1 ]       if( coded_sub_block_flag[ xS ][ yS ] && (n > 0 || !inferSbDcSigCoeffFlag ) ) {        sig_coeff_flag[ xC ][ yC ]ae(v)        remBinsPass1− −        if( sig_coeff_flag[ xC ][ yC ] )        inferSbDcSigCoeffFlag = 0       }       if( sig_coeff_flag[ xC][ yC ] ) {        numSigCoeff++        abs_level_gt1_flag[ n ] ae(v)       remBinsPass1        if( abs_level_gt1_flag[ n ] ) {        par_level_flag[ n ] ae(v)         remBinsPass1− −         if(remBinsPass2 > 0 ) {          remBinsPass2− −          if( remBinsPass2= = 0 )           firstPosMode1 = n 1         }        }        if(lastSigScanPosSb = = −1 )         lastSigScanPosSb = n       firstSigScanPosSb = n       }       AbsLevelPass1[ xC ][ yC ] =        sig_coeff_flag[ xC ][ yC ] + par_level_flag[ n ] +abs_level_gt1_flag[ n ]       if( dep_quant_enabled_flag )        QState= QStateTransTable[ QState ][ AbsLevelPass1[ xC ][ yC ] & 1 ]       if(remBinsPass1 < 3 )        firstPosMode2 = n − 1      }      if(firstPosMode1 < firstPosMode2 )       firstPosMode1 − firstPosMode2     for( n = numSbCoeff − 1; n >= firstPosMode2; n− − )       if(abs_level_gt1_flag[ n ] )        abs_level_gt3_flag[ n ] ae(v)      for(n = numSbCoeff − 1; n >= firstPosMode1; n− − ) {       xC = ( xS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]      yC = ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 1 ]       if( abs_level_gt3_flag[ n ] )       abs_remainder[ n ] ae(v)       AbsLevel[ xC ][ yC ] =AbsLevelPass1[ xC ][ yC ] +              2 * ( abs_level_gt3_flag[ n ] +abs_remainder[ n ] )      }      for( n = firstPosMode1; n >firstPosMode2; n− − ) {       xC = ( xS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 0 ]       yC = ( yS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]       if(abs_level_gt1_flag[ n ] )        abs_remainder[ n ] ae(v)      AbsLevel[ xC ][ yC ] = AbsLevelPass1[ xC ][ yC ] + 2 *abs_remainder[ n ]      }      for( n = firstPosMode2; n >= 0; n ) {      xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 0 ]       yC = ( yS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 1 ]       dec_abs_level[ n ] ae(v)      if(AbsLevel[ xC ][ yC ] > 0 )        firstSigScanPosSb = n      if( dep_quant_enabled_flag )        QState = QStateTransTable[QState ][ AbsLevel[ xC ][ yC ] & 1 ]      }      if(dep_quant_enabled_flag || !sign_data_hiding_enabled_flag )      signHidden = 0      else       signHidden = ( lastSigScanPosSbfirstSigScanPosSb > 3 ? 1 : 0 )      for( n = numSbCoeff − 1; n >− 0; n−− ) {       xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 0 ]       yC = ( yS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 1 ]       if( sig_coeff_flag[ xC ][ yC] &&        ( !signHidden || ( n != firstSigScanPosSb ) ) )       coeff_sign_flag[ n ] ae(v)      }      if( dep_quant_enabled_flag) {       QState = startQStateSb       for( n = numSbCoeff 1; n >= 0; n) {        xC = ( xS << log2SbSize ) +          DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 0 ]        yC = ( yS << log2SbSize ) +         DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]        if(sig_coeff_flag[ xC ][ yC ] )         TransCoeffLevel[ x0 ][ y0 ][ cIdx][ xC ][ yC ] =           ( 2 * AbsLevel[ xC ][ yC ] − ( QState > 1 ? 1: 0 ) ) *           ( 1 − 2 * coeff_sign_flag[ n ] )        QState =QStateTransTable[ QState ][ par_level_flag[ n ] ]      } else {      sumAbsLevel = 0       for( n = numSbCoeff − 1; n >= 0; n− − ) {       xC = ( xS << log2SbSize ) +          DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 0 ]        yC = ( yS << log2SbSize ) +         DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]        if(sig_coeff_flag[ xC ][ yC ] ) {         TransCoeffLevel[ x0 ][ y0 ][ cIdx][ xC ][ yC ] =           AbsLevel[ xC ][ yC ] * ( 1 − 2 *coeff_sign_flag[ n ] )         if( signHidden ) {          sumAbsLevel+= AbsLevel[ xC ][ yC ]          if( ( n = = firstSigScanPosSb ) && (sumAbsLevel % 2 ) = = 1 ) )           TransCoeffLevel[ x0 ][ y0 ][ cIdx][ xC ][ yC ] =             TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][yC ]         }        }       }      }     }     if( tu_mts_flag[ x0 ][y0 ] && ( cIdx = = 0 ) )      mts_idx[ x0 ][ y0 ][ cIdx ] ae(v)    }

transform_skip_flag indicates whether a transform is skipped withrespect to an associated block. transform_skip_flag may be a syntaxelement of a transform skip flag. The associated block may be a codingblock (CB) or a transform block (TB). Regarding transformation (andquantization) and residual coding procedures, a CB and a TB may beinterchangeably used. For example, as described above, residual samplesmay be derived for a CB, and (quantized) transform coefficients may bederived through transformation and quantization of the residual samples.Further, information (e.g., syntax elements) efficiently indicating theposition, size, sign, and the like of the (quantized) transformcoefficients may be generated and signaled through a residual codingprocedure. The quantized transform coefficients may be simply referredto as transform coefficients. Generally, when a CB is not larger than amaximum TB, the size of the CB may be the same as the size of the TB, inwhich case a target block to be subjected to transformation (andquantization) and residual coding may be referred to as a CB or a TB.However, when a CB is greater than a maximum TB, a target block to besubjected to transformation (and quantization) and residual coding maybe referred to as a TB. Hereinafter, although syntax elements related toresidual coding are described as being signaled by a unit of a transformblock (TB), which is for illustration, a TB may be interchangeably usedwith a coding block (CB).

In an embodiment, the encoding apparatus may encode (x, y) positioninformation on the last non-zero transform coefficient in a transformblock based on syntax elements last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, andlast_sig_coeff_y_suffix. Specifically, last_sig_coeff_x_prefix indicatesa prefix of a column position of the last significant coefficient in ascan order in the transform block, last_sig_coeff_y_prefix indicates aprefix of a row position of the last significant coefficient in the scanorder in the transform block, last_sig_coeff_x_suffix indicates a suffixof the column position of the last significant coefficient in the scanorder in the transform block, and last_sig_coeff_y_suffix indicates asuffix of the row position of the last significant coefficient in thescan order in the transform block. Here, the significant coefficient mayrefer to the non-zero coefficient. Further, the scan order may be aright upward diagonal scan order. Alternatively, the scan order may be ahorizontal scan order or a vertical scan order. The scan order may bedetermined based on whether inter/inter prediction is applied to atarget block (CB or CB including a TB) and/or a specific intra/interprediction mode.

Next, the encoding apparatus may partition the transform block into 4×4subblocks and may then indicate whether a non-zero coefficient exists ina current subblock using a 1-bit syntax element coded_sub_block_flag foreach 4×4 subblock.

When the value of coded_sub_block_flag is 0, there is no moreinformation to be transmitted, and thus the encoding apparatus may endan encoding process for the current subblock. However, when the value ofcoded_sub_block_flag is 1, the encoding apparatus may continue theencoding process for sig_coeff_flag. Since a subblock including the lastnon-zero coefficient does not require encoding of coded_sub_block_flagand a subblock including DC information on the transform block is highlylikely to include a non-zero coefficient, coded_sub_block_flag may beassumed to be 1 without being coded.

When the value of coded_sub_block_flag is 1 and thus it is determinedthat a non-zero coefficient exists in the current subblock, the encodingapparatus may encode sig_coeff_flag having a binary value according tothe inverse scan order. The encoding apparatus may encode the 1-bitsyntax element sig_coeff_flag for each transform coefficient accordingto the scan order. When the value of a transform coefficient at acurrent scanning position is not 0, the value of sig_coeff_flag maybe 1. Here, in the subblock including the last non-zero coefficient,sig_coeff_flag does not need to be encoded for the last non-zerocoefficient, and thus an encoding process for the subblock may beomitted. Level information encoding may be performed only whensig_coeff_flag is 1, and four syntax elements may be used in a levelinformation encoding process. Specifically, each sig_coeff_flag[xC][yC]may indicate whether the level (value) of a transform coefficient ateach transform coefficient position (xC, yC) in the current TB isnon-zero. In an embodiment, sig_coeff_flag may be an example of a syntaxelement of a significant coefficient flag indicating whether a quantizedtransform coefficient is a non-zero significant coefficient.

A level value remaining after encoding of sig_coeff_flag may be derivedaccording to the following equation. That is, a syntax elementremAbsLevel indicating a level value to be encoded may be derivedaccording to the following equation.

$\begin{matrix}{{remAbsLevel} = {{{coeff}} - 1}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

Here, coeff denotes an actual transform coefficient value.

Further, abs_level_gt1_flag may indicate whether remAbsLevel′ at ascanning position (n) is greater than 1. For example, when the value ofabs_level_gt1_flag is 0, the absolute value of a transform coefficientat the position may be 1. When the value of the abs_level_gt1_flag is 1,remAbsLevel indicating the level value to be encoded may be derivedaccording to the following equation.

$\begin{matrix}{{remAbsLevel} = {{remAbsLevel} - 1}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

The value of the least significant coefficient (LSB) of remAbsLevelillustrated in Equation 2 may be encoded through par_level_flagaccording to in Equation 3.

$\begin{matrix}{{{{par}{\_ level}}{\_ flag}} = {{{remAbsLevel}\&}\mspace{14mu} 1}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

Here, par_level_flag[n] may indicate the parity of a transformcoefficient level (value) at the scanning position n.

The transform coefficient level value remAbsLevel to be encoded afterencoding par_leve_flag may be updated according to the followingequation.

$\begin{matrix}{{{remAbsLevel}^{\prime} = {remAbsLevel}}\operatorname{>>}1} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

abs_level_gt3_flag may indicate whether remAbsLevel′ at the scanningposition n is greater than 3. abs_remainder may be encoded only whenrem_abs_gt3_flag is 1. A relationship between coeff, which is an actualtransform coefficient value, and each syntax element may be expressed bythe following equation.

$\begin{matrix}{{{coeff}} = {{{{sig}\_{coeff}}{\_ flag}} + {{abs\_ level}{\_{gt}1}{\_ flag}} + {{par\_ level}{\_ flag}} + {2*( {{{abs\_ level}{\_{gt}3}{\_ flag}} + {abs\_ remainder}} )}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

The following table shows examples related to Equation 5.

TABLE 2 abs_remainder/ |coeff| sig_coeff_flag abs_level_gt1_flagpar_level_flag abs_level_gt3_flag dec_abs_level 0 0 1 1 0 2 1 1 0 3 1 11 0 4 1 1 0 1 0 5 1 1 1 1 0 6 1 1 0 1 1 7 1 1 1 1 1 8 1 1 0 1 2 9 1 1 11 2 10 1 1 0 1 3 11 1 1 1 1 3 . . . . . . . . . . . .

|coeff| indicates a transform coefficient level (value) and may beexpressed as AbsLevel for a transform coefficient. The sign of eachcoefficient may be encoded using a 1-bit symbol coeff_sign_flag.

dec_abs_level may indicate an intermediate value coded with aGolomb-Rice code at the scanning position n. dec_abs_level may besignaled for a scanning position that satisfies a condition disclosed inTable 2, in which case the absolute value AbsLevel (i.e., |coeff|) ofthe transform coefficient may be derived as one of 0, dec_abs_level+1,and dec_abs+ depending on a condition.

coeff_sign_flag may indicate the sign of the transform coefficient levelat the scanning position n. That is, coeff_sign_flag may indicate thesign of the transform coefficient at the scanning position n.

mts_idx may indicate transform kernels applied to residual samples inthe current transform block in a horizontal direction and a verticaldirection.

FIG. 5 illustrates an example of transform coefficients in a 4×4 block.

The 4×4 block of FIG. 5 shows an example of quantized coefficients. Theblock shown in FIG. 5 may be a 4×4 transform block or a 4×4 subblock ofan 8×8, 16×16, 32×32, or 64×64 transform block. The 4×4 block of FIG. 5may represent a luma block or a chroma block.

For example, the result of encoding coefficients scanned in anantidiagonal order of FIG. 5 may be shown in the following table.

TABLE 3 scan_pos 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 coefficients 0 00 0 1 −1 0 2 0 3 −2 −3 4 6 −7 10 sig_coeff_flag 0 0 0 0 1 1 0 1 0 1 1 11 1 abs_level_gt1 _flag 0 0 1 1 1 1 1 1 par_level_flag 0 1 0 1 0 0abs_level_gt3_flag 1 1 abs_remainder 0 1 dec_abs_level 7 10coeff_sign_flag 0 0 0 0 0 1 0 0 0 0 1 1 0 0 1 0

In Table 3, scan_pos indicates the position of a coefficient accordingto antidiagonal scanning scan_pos 15 may be a transform coefficientscanned first, that is, on the bottom-right corner, in the 4×4 block,and scan_pos 0 may be a transform coefficient scanned last, that is, onthe top-left corner. In an embodiment, scan_pos may be referred to as ascanning position. For example, scan_pos 0 may be referred to asscanning position 0.

CABAC provides high performance but has poor throughput. This is due toa regular coding engine of CABAC, and regular encoding (i.e., encodingthrough the regular coding engine of CABAC) exhibits high datadependency because using a probability state and range updated throughencoding of a previous bin, and may take a substantial time to read theprobability range and to determine a current state. The poor throughputof CABAC may be solved by limiting the number of context-coded bins. Forexample, as shown in Table 1, the sum of bins used to expresssig_coeff_flag, abs_level_gt1_flag, and par_level_flag may be limited toa number according to the size of a corresponding block. Specifically,when the block is a 4×4 block, the sum of bins for sig_coeff_flag,abs_level_gt1_flag, and par_level_flag may be limited to 28, and whenthe block is a 2×2 block, the sum of bins for sig_coeff_flag,abs_level_gt1_flag, and par_level_flag may be limited to 6. The limitednumber of bins may be expressed as remBinsPass1. Further, the number ofcontext-coded bins for abs_level_gt3_flag may be limited to a numberaccording to the size of a corresponding block. For example, when theblock is a 4×4 block, the number of bins for abs_level_gt3_flag may belimited to 4, and when the block is a 2×2 block, the number of bins forabs_level_gt3_flag may be limited to 2. The limited number of bins forabs_level_gt3_flag may be expressed as remBinsPass2. In this case, whenall of the limited number of context-coded bins are used to encode acontext element, an encoding apparatus may binarize remainingcoefficients through a binarization method for the coefficients, whichwill be described later, rather than using CAB AC and may perform bypassencoding thereon.

As described above, when an input signal is a syntax element rather thana binary value, the encoding apparatus may convert the input signal intoa binary value by binarizing the value of the input signal. A decodingapparatus may decode the syntax element to derive a binarized value(i.e., a binarized bin) of the syntax element and may debinarize thebinarized value to derive the value of the syntax element. Thebinarization process may be performed using a truncated Rice (TR)binarization process, a kth order Exp-Golomb (EGk) binarization process,or a fixed-length (FL) binarization process, which will be describedlater. The debinarization process may be performed based on the TRbinarization process, the EGk binarization process, or the FLbinarization process, thereby deriving the value of the syntax element.

For example, the TR binarization process may be performed as follows.

Input to the TR binarization process may be a request for TRbinarization and cMax and cRiceParam for the syntax element. Output ofthe TR binarization process may be TR binarization associating a valuesymbolVal with a corresponding bin string.

Specifically, for example, when there is a suffix bin string for thesyntax element, a TR bin string for the syntax element may be aconcatenation of a prefix bin string and the suffix bin string, and whenthere is no suffix bin string, the TR bin string for the syntax elementmay be the prefix bin string. For example, the prefix bin string may bederived as follows.

The prefix value of symbolVal for the syntax element may be derivedaccording to the following equation.

$\begin{matrix}{{{prefixVal} = {symbolVal}}\operatorname{>>}{cRiceParam}} & \lbrack {{Equation}\mspace{14mu} 6} \rbrack\end{matrix}$

Here, prefixVal may denote the prefix value of symbolVal. A prefix(i.e., the prefix bin string) of the TR bin string of the syntax elementmay be derived as follows.

For example, when prefixVal is less than cMax>>cRiceParam, the prefixbin string may be a bit string having a length of prefixVal+1 indexed bybinIdx. That is, when prefixVal is less than cMax>>cRiceParam, theprefix bin string may be a bit string of prefixVal+1 bit indicated bybinIdx. A bin for binIdx less than prefixVal may be equal to 1. A binfor binIdx equal to prefixVal may be equal to 0.

For example, a bin string derived by unary binarization of prefixVal maybe as shown in the following table.

TABLE 4 prefixVal Bin string 0 0 1 1 0 2 1 1 0 3 1 1 1 0 4 1 1 1 1 0 5 11 1 1 1 0 . . . binIdx 0 1 2 3 4 5

When prefixVal is not less than cMax>>cRiceParam, the prefix bin stringmay be a bit string having a length of cMax>>cRiceParam and includingall bins equal to 1.

When cMax is greater than symbolVal and cRiceParam is greater than 0, asuffix bin string of the TR bin string may exist. For example, thesuffix bin string may be derived as follows.

The suffix value of symbolVal for the syntax element may be derivedaccording to the following equation.

$\begin{matrix}{{suffixVal} = {{symbolVal} - ( {({prefixVal})\mspace{14mu}{\operatorname{<<}{cRiceParam}}} )}} & \lbrack {{Equation}\mspace{14mu} 7} \rbrack\end{matrix}$

Here, suffixVal may denote the suffix value of symbolVal.

A suffix (i.e., the suffix bin string) of the TR bin string may bederived based on an FL binarization process for suffixVal with a cMaxvalue equal to (1<<cRiceParam)−1.

When the value of cRiceParam as an input parameter is 0, the TRbinarization may be exactly a truncated unary binarization and mayalways use a cMax value equal to the largest possible value of thesyntax element to be decoded.

Further, for example, the EGk binarization process may be performed asfollows. A syntax element coded as ue(v) may be an Exp-Golomb-codedsyntax element.

In one example, a 0th order Exp-Golomb (EG0) binarization process may beperformed as follows.

A parsing process for the syntax element may start with reading bitsstarting at a current position in the bitstream and including a firstnon-zero bit and counting the number of leading bits that are equal to0. This process may be specified as follows.

TABLE 5 leadingZeroBits = −1 for( b = 0; !b; leadingZeroBits++ )  b =read_bits( 1 )

A variable codeNum may be derived as follows

$\begin{matrix}{{codeNum} = {2^{leadingZeroBits} - 1 + {{read\_ bits}({leadingZeroBits})}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Here, a value returned from read_bits(leadingZeroBits), that is, a valueindicated by read_bits(leadingZeroBits), may be interpreted as a binaryrepresentation of an unsigned integer with a most significant bitwritten first.

The structure of an Exp-Golomb code in which the bit string is separatedinto “prefix” and “suffix” bits may be as illustrated in the followingtable.

TABLE 6 Bit string form Range of codeNum 1 0 0 1 x₀ 1 . . . 2 0 0 1 x₁x₀ 3 . . . 6 0 0 0 1 x₂ x₁ x₀  7 . . . 14 0 0 0 0 1 x₃ x₂ x₁ x₀ 15 . . .30 0 0 0 0 0 1 x₄ x₃ x₂ x₁ x₀ 31 . . . 62 . . . . . .

A “prefix” bit may be a bit parsed as specified above for computation ofleadingZeroBits and may be denoted by 0 or 1 in the bit string in Table6. That is, a bit string starting with 0 or 1 in Table 6 may denote aprefix bit string. A “suffix” bit may be a bit parsed in computation ofcodeNum and may be denoted by xi in Table 6. That is, a bit stringstarting with xi in Table 6 may denote a suffix bit string. Here, i maybe a value ranging from 0 to LeadingZeroBits−1. Further, each xi may beequal to 0 or 1.

A bit string allocated to codeNum may be as illustrated in the followingtable.

TABLE 7 Bit string codeNum 1 0 0 1 0 1 0 1 1 2 0 0 1 0 0 3 0 0 1 0 1 4 00 1 1 0 5 0 0 1 1 1 6 0 0 0 1 0 0 0 7 0 0 0 1 0 0 1 8 0 0 0 1 0 1 0 9 .. . . . .

When a descriptor of the syntax element is ue(v), that is, when thesyntax element is coded as ue(v), the value of the syntax element may beequal to codeNum.

In addition, for example, the EGk binarization process may be performedas follows.

Input to the EGk binarization process may be a request for EGkbinarization. Output of the EGk binarization process may be EGkbinarization associating a value symbolVal with a corresponding binstring.

The bit string of the EGk binarization process for symbolVal may bederived as follows.

TABLE 8   absV = Abs( symbolVal ) stopLoop = 0 do  if( absV >= ( 1 << k) ) {   put( 1 )   absV = absV − ( 1 << k )   k++  } else {   put( 0 )  while( k− − )    put( ( absV >> k ) & 1 )   stopLoop = 1  } while(!stopLoop )

Referring to Table 8, a binary value X may be added to the end of thebin string through each call of put(X). Here, X may be equal to 0 or 1.

In addition, for example, the FL binarization process may be performedas follows.

Input to the FL binarization process may be a request for FLbinarization and cMax for the syntax element. Output of the FLbinarization process may be FL binarization associating a valuesymbolVal with a corresponding bin string.

FL binarization may be constructed using a bit string having the numberof bits corresponding to a fixed length of the symbol value symbolVal.Here, the fixed-length bit may be an unsigned integer bit string. Thatis, a bit string for the symbol value symbolVal may be derived throughFL binarization, and the bit length (i.e., the number of bits) of thebit string may be a fixed length.

For example, the fixed length may be derived as follows.

$\begin{matrix}{{fixedLength} = {{Ceil}( {{Log2}( {{c{Max}} + 1} )} )}} & \lbrack {{Equation}\mspace{14mu} 9} \rbrack\end{matrix}$

Indexing of bins for FL binarization may be performed using a valueincreasing from the most significant bit to the least significant bit.For example, a bin index related to the most significant bit may bebinIdx=0.

For example, a binarization process for the syntax element abs_remainderof the residual information may be performed as follows.

Inputs to the binarization process for abs_remainder and dec_abs_levelmay be a request for binarization of a syntax element abs_remainder[n]or a syntax element dec_abs_level[n], a color component cIdx, a lumaposition (x0, y0), a current coefficient scanning position (xC, yC), log2TbWidth, which is the binary logarithm of the width of the transformblock, and log 2TbHeight, which is the binary logarithm of the height ofthe transform block. The luma position (x0, y0) may refer to thetop-left sample of the current luma transform block relative to thetop-left luma sample of the picture.

Output of the binarization process for abs_remainder (or dec_abs_level)may be binarization of abs_remainder (or the dec_abs_level) (i.e., abinarized bin string of abs_remainder (or dec_abs_level)). Available binstrings for abs_remainder (or dec_abs_level) may be derived through thebinarization process.

cRiceParam, a Rice parameter for abs_remainder (or dec_abs_level), maybe derived by a Rice parameter derivation process performed with thecolor component cIdx, the luma position (x0, y0), the currentcoefficient scanning position (xC, yC), and log 2TbHeight, which is thebinary logarithm of the height of the transform block as inputs. Adetailed description of the Rice parameter derivation process will bedescribed later.

For example, cMax for abs_remainder (or dec_abs_level) may be derivedbased on the Rice parameter cRiceParam. cMax may be derived as follows.

$\begin{matrix}{{c{Max}} = {( {{{cRiceParam}=={1\mspace{14mu}?\mspace{14mu} 6}}:7} ){\operatorname{<<}{cRiceParam}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

Referring to Equation 10, when the value of cRiceParam is 1, cMax may bederived as 6<<cRiceParam, and when the value of cRiceParam is not 1,cMax may be derived as 7<<cRiceParam.

The binarization of abs_remainder (or dec_abs_level), that is, the binstring of the abs_remainder (or dec_abs_level), may be a concatenationof a prefix bin string and a suffix bin string when the suffix binstring is present. When there is no suffix bin string, the bin string ofabs_remainder (or dec_abs_level) may be the prefix bin string.

For example, the prefix bin string may be derived as follows.

The prefix value of abs_remainder, prefixVal, may be derived as follows.

$\begin{matrix}{{prefixVal} = {{Min}( {{c{Max}},{{abs\_ remainder}\lbrack n\rbrack}} )}} & \lbrack {{Equation}\mspace{14mu} 11} \rbrack\end{matrix}$

The prefix of the bin string of abs_remainder (i.e., the prefix binstring) may be derived through a TR binarization process for prefixValwith cMax and cRiceParam as inputs.

When the prefix bin string is equal to a bit string including all bitsequal to 1 and having a bit length of 4, a suffix bin string of the binstring of abs_remainder may exist and may be derived as follows.

The suffix value of abs_remainder, suffixVal, may be derived as follows.

$\begin{matrix}{{suffixVal} = {{{abs\_ remainder}\lbrack n\rbrack}{c{Max}}}} & \lbrack {{Equation}\mspace{14mu} 12} \rbrack\end{matrix}$

The suffix bin string of the bin string of abs_remainder may be derivedthrough an EGk binarization process for suffixVal with k set tocRiceParam+1.

The foregoing Rice parameter derivation process may be as follows.

Inputs to the Rice parameter derivation process may be the colorcomponent index cIdx, the luma position (x0, y0), the currentcoefficient scanning position (xC, yC), the binary logarithm of thewidth of the transform block, which is log 2TbWidth, and the binarylogarithm of the height of the transform block, which is log 2TbHeight.The luma position (x0, y0) may refer to the top-left sample of thecurrent luma transform block relative to the top-left luma sample of thepicture. Output of the Rice parameter derivation process may be the riceparameter, cRiceParam.

For example, given the syntax elements sig_coeff_flag[x][y] and arrayAbsLevel[x][C] for the transform block with the component index cIdx andthe top-left luma position (x0, y0), a variable locSumAbs may be derivedas a pseudo code specified in the following table.

TABLE 9 locSumAbs = 0 if( xC < (1 << log2TbWidth) − 1 ) {  locSumAbs +=AbsLevel[ xC + 1 ][ yC ] − sig_coeff_flag[ xC + 1 ][ yC ]  if( xC < (1<< log2TbWidth) − 2 )   locSumAbs += AbsLevel[ xC + 2 ][ yC ] −sig_coeff_flag[ xC + 2 ][ yC ]  if( yC < (1 << 1og2TbHeight) − 1 )  locSumAbs += AbsLevel[ xC + 1 ][ yC + 1] − sig_coeff_flag[ xC + 1 ][yC + 1 ] } if( yC < (1 << log2TbHeight) − 1 ) {  locSumAbs += AbsLevel[xC ][ yC + 1 ] − sig_coeff_flag[ xC ][ yC + 1 ]  if( yC < (1 <<log2TbHeight) − 2 )   locSumAbsPass1 += AbsLevelPass1 [ xC ][ yC + 2 ] −sig_coeff_flag[ xC ][ yC + 2 ] }

The Rice parameter, cRiceParam, may be derived as follows.

For example, when locSumAbs is less than 12, cRiceParam may be set to 0.Otherwise, when locSumAbs is less than 25 (i.e., when locSumAbs is equalto or greater than 12 and is less than 25), cRiceParam may be set to 1.Otherwise, (i.e., when locSumAbs is equal to or greater than 25),cRiceParam may be set to 2.

Unlike the foregoing embodiment of transmitting the syntax elements, amethod of signaling tu_mts_idx may be proposed.

Specifically, the proposed method of signaling tu_mts_idx may becompared with an existing method of signaling tu_mts_idx according toVVC Draft 3 as follows.

TABLE 10 WC Draft 3 Proposed transform_unit( ) transform_unit( ) tu_cbf_luma  tu_cbf_luma ...  if( ... tu_cbf_luma &&  if( ...tu_cbf_luma &&   ( tbWidth <= 32 ) &&   ( tbWidth <= 32 ) &&   (tbHeight <= 32 ) ... )   ( tbHeight <= 32 ) ... )   tu_mts_flag  tu_mts_idx residual_coding( cIdx )  if( ( cIdx ! = 0 || !tu_mts_flag )&&   ( log2TbWidth <= 2 ) &&   ( log2TbHeight <= 2 ) )  transform_skip_flag[ cIdx ]  ... /* coefficient parsing */ ...  if(tu_mts_flag && cIdx = = 0 )   mts_idx

As illustrated in Table 10, according to the existing method, an MTSflag for the current block may be parsed, followed by parsing atransform skip flag and then coding an MTS index. Here, the MTS indexmay be coded by fixed-length binarization, and a fixed bit length forthe MTS index may be 2.

However, according to the proposed method, the MTS index may be codedwithout separately parsing the transform skip flag and the MTS flag, andtruncated unary binarization may be used for coding the MTS index. Here,the MTS index may indicate whether a transform is applied to residualinformation on the current block and may indicate whether the MTS isapplied. That is, the proposed method may propose signaling thetransform skip flag, the MTS flag, and the MTS index as one syntaxelement. In the proposed method, a first bin of the MTS index mayindicate whether the transform is applied to the residual information onthe current block, and a second bin of the MTS index may indicatewhether the MTS is applied and an applied transform kernel.

Semantics and a binarization value indicated by the value of the MTSindex in the proposed method may be as illustrated in the followingtable.

TABLE 11 binarization transform type MTS & TS MTS TS tu_mts_idxhorizontal vertical enabled enabled enabled 0 DCT-II DCT-II 0 0 0 1 SKIPSKIP 10 — 1 2 DST-VII DST-VII 110 10 — 3 DCT-VIII DST-VII 1110 110 — 4DST-VII DCT-VIII 11110 1110 — 5 DCT-VIII DCT-VIII 11111 1111 —

For example, when the value of the MTS index is 0, the MTS index mayindicate that a transform is applied to the current block, that no MTSis applied, and that a horizontal transform kernel type and a verticaltransform kernel type are DCT-2. When the value of the MTS index is 1,the MTS index may indicate that no transform is applied to the currentblock (i.e., may also indicate that no MTS is applied and may notindicate a transform kernel type). When the value of the MTS index is 2,the MTS index may indicate that a transform and an MTS are applied tothe current block and that a horizontal transform kernel type and avertical transform kernel type are DST-7. When the value of the MTSindex is 3, the MTS index may indicate that a transform and an MTS areapplied to the current block and that a horizontal transform kernel typeis DCT-8 and a vertical transform kernel type is DST-7. When the valueof the MTS index is 4, the MTS index may indicate that a transform andan MTS are applied to the current block and that a horizontal transformkernel type is DST-7 and a vertical transform kernel type is DCT-8. Whenthe value of the MTS index is 5, the MTS index may indicate that atransform and an MTS are applied to the current block and that ahorizontal transform kernel type and a vertical transform kernel typeare DCT-8.

In an alternative example, semantics and a binarization value indicatedby the value of the MTS index may be as illustrated in the followingtable.

TABLE 12 binarization transform type MTS & TS MTS TS tu_mts_idxhorizontal vertical enabled enabled enabled 0 SKIP SKIP 0 — 0 1 DCT-IIDCT-II 10 0 1 2 DST-VII DST-VII 110 10 — 3 DCT-VIII DST-VII 1110 110 — 4DST-VII DCT-VIII 11110 1110 — 5 DCT-VIII DCT-VIII 11111 1111 —

For example, when the value of the MTS index is 0, the MTS index mayindicate that no transform is applied to the current block (i.e., mayalso indicate that no MTS is applied and may not indicate a transformkernel type). When the value of the MTS index is 1, the MTS index mayindicate that a transform is applied to the current block, that no MTSis applied thereto, and that a horizontal transform kernel type and avertical transform kernel type are DCT-2. When the value of the MTSindex is 2, the MTS index may indicate that a transform and a MTS areapplied to the current block and that a horizontal transform kernel typeand a vertical transform kernel type are DST-7. When the value of theMTS index is 3, the MTS index may indicate that a transform and a MTSare applied to the current block and that a horizontal transform kerneltype is DCT-8 and a vertical transform kernel type is DST-7. When thevalue of the MTS index is 4, the MTS index may indicate that a transformand a MTS are applied to the current block and that a horizontaltransform kernel type is DST-7, and a vertical transform kernel type isDCT-8. When the value of the MTS index is 5, the MTS index may indicatethat a transform and a MTS are applied to the current block and that ahorizontal transform kernel type and a vertical transform kernel typeare DCT-8.

The number of context models may not be changed, and a method fordesignating a context index increment, ctxInc, for each bin oftu_mts_idx may be as illustrated in the following table.

TABLE 13 binIdx Syntax element 0 1 2 3 4 >= 5 tu_mts_idx 0 1 . . . 6 7 89 na (MTS & TS) (1 + cqtDepth) tu_mts_idx 1 . . . 6 7 8 9 na na (MTS)(1 + cqtDepth) tu_mts_idx 0 na na na na na (TS)

Further, the present disclosure proposes a method of modifying thefollowing details in the existing residual coding method in order toadapt the statistics and signal characteristics of a transform skiplevel, which represents a quantized prediction residual (i.e., aresidual in a spatial domain), to residual coding.

No last non-zero transform coefficient position: Since a residual signal(i.e., a residual sample) reflects a spatial residual after predictionand no energy compaction by a transform is performed for a transformskip, a high probability for a trailing zero or an insignificant levelat the bottom right corner of a transform block may not occur anymore.Thus, in this case, signaling information on the scanning position ofthe last non-zero transform coefficient may be omitted. Instead, a firstsubblock to be coded first may be the bottom-right subblock in thetransform block. The non-zero transform coefficient may also be referredto as a significant coefficient.

Subblock CBF: The absence of signaling of the information on thescanning position of the last non-zero transform coefficient requiresapplication of a transform skip and modification of CBF signaling of asubblock with coded_sub_block_flag as follows.

Due to quantization, the aforementioned sequence of the insignificantlevel may still occur locally inside a transform block. Thus, theinformation on the scanning position of the last non-zero transformcoefficient may be removed as described above, and coded_sub_block_flagmay be coded for all subblocks.

coded_sub_block_flag for a subblock (top-left subblock) covering a DCfrequency position may denote a special case. For example, in VVC Draft3, coded_sub_block_flag for the top-left subblock may always be inferredto be equal to 1 without being signaled. When the scanning position ofthe last non-zero transform coefficient corresponds to the position of asubblock other than the top-left subblock, it may be indicated thatthere is at least one significant level outside the DC subblock (i.e.,the top-left subblock). Consequently, the DC subblock may include only azero/non-significant level although coded_sub_block_flag for the DCsubblock is inferred to be equal to 1. As described above, when thetransform skip is applied to the current block and there is noinformation on the scanning position of the last non-zero transformcoefficient, coded_sub_block_flag for each subblock may be signaled.Here, the coded_sub_block_flag for the DC subblock may also be includedexcept when coded_sub_block_flag for all subblocks other than the DCsubblock is already equal to 0. In this case, coded_sub_block_flag forthe DC subblock may be inferred to be equal to 1 (inferDcSbCbf=1). Sincethere needs to be at least one significant level in the DC subblock,when all sig_coeff_flag other than sig_coeff_flag for a first positionof (0, 0) in the DC subblock is equal to 0, sig_coeff_flag for the firstposition of (0,0) may be inferred to be equal to 1, without beingsignaled (inferSbDcSigCoeffFlag=1).

Context modeling for coded_sub_block_flag may be changed. For example, acontext model index may be calculated using the sum ofcoded_sub_block_flag of a right subblock of the current subblock andcoded_sub_block_flag of a bottom subblock of the current subblock and alogical disjunction thereof.

sig_coeff_flag context modeling: A local template in sig_coeff_flagcontext modeling may be modified to include only a right position (NB0)and a lower position (NB1) of the current scanning position. A contextmodel offset may be derived as the number ofsig_coeff_flag[NB0]+sig_coeff_flag[NB1] of significant neighboringpositions. Therefore, a selection of different context sets depending ona diagonal d of the current transform block may be removed. As a result,three context models and a single context model may be configured tocode sig_coeff_flag flag.

abs_level_gt1_flag and par_level_flag context modeling: A single contextmodel may be employed for abs_level_gt1_flag and par_level_flag.

abs_remainder coding: Although the empirical distribution of transformskip residual absolute levels still fits a Laplacian or geometricaldistribution, instationarities greater than transform coefficientabsolute levels may exist. Particularly, variance within a window ofconsecutive realization may be higher for residual absolute levels.Accordingly, the binarization of abs_remainder and context modeling maybe modified as follows.

For example, a higher cutoff value may be used in the binarization ofabs_remainder. Accordingly, a transition point from coding usingsig_coeff_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gt3_flag to a Rice code for abs_remainder and a dedicatedcontext model for each bin position may yield higher compressionefficiency. Increasing the cutoff may result in more “greater than X”flags (e.g., abs_level_gt5_flag, abs_level_gt1_flag, or the like) untila cutoff is reached. The cutoff may be fixed to 5 (numGtFlags=5).

A template for deriving a Rice parameter may be modified. That is, onlya right neighboring position and a bottom neighboring position of thecurrent scanning position may be considered as the local template forsig_coeff_flag context modeling.

coeff_sign_flag context modeling: Due to instationarities inside asequence of signs and a prediction residual being often biased,sign-related information may be coded using a context model even whenthe global empirical distribution is almost uniformly distributed. Asingle-dedicated context model may be used for coding the sign-relatedinformation, and the sign-related information may be parsed aftersig_coeff_flag and may be maintained along with all context-coded bins.

Reduction of context-coded bins: Transmission of syntax elements, i.e.,sig_coeff_flag, abs_level_gt1_flag and par_level_flag, for a firstscanning pass may be unchanged. However, a limitation on the specificnumber of context-coded bins per sample (CCBs) may be removed and may beadjusted differently. A reduction of CCBs may be derived by specifying amode with CCB>k as invalid. Here, k may be a positive integer. Forexample, in a regular level coding mode, k=2. The foregoing limitationmay correspond to a reduction of a quantization space.

Syntax elements related to residual data coded by applying the foregoingmodifications may be as illustrated in the following table.

TABLE 14 Descriptor residual_ts_coding( x0, y0, log2TbWidth,log2TbHeight, cIdx ) {  log2SbSize = ( Min( log2TbWidth, log2TbHeight )< 2 ? 1 : 2 )  numSbCoeff = 1 << ( log2SbSize << 1 )  lastSubBlock = ( 1<< ( log2TbWidth + log2TbHeight − 2 * log2SbSize ) ) − 1 /* Loop oversubblocks from last to the top-left (DC) subblock */  inferDcSbCbf = 1 for( i = lastSubBlock; i >= 0; i− − ) {  xS = DiagScanOrder[log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize ][ lastSubBlock ][0 ]  yS = DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight −log2SbSize ][ lastSubBlock ][ 1 ]  if( ( i > 0 || !inferDcSbCbf )  coded_sub_block_flag[ xS ][ yS ] ae(v)  if( coded_sub_block_flag[ xS][ yS ] && i > 0 )   inferDcSbCbf = 0  }  /* First scan pass */ inferSbDcSigCoeffFlag = 1  for( n = ( i = = numSbCoeff − 1; n >= 0; n−− ) {   xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 0 ]   yC = ( yS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 1 ]   if( coded_sub_block_flag[ xS ][yS ] && ( n > 0 || !inferSbDcSigCoeffFlag ) ) {    sig_coeff_flag[ xC ][yC ] ae(v)    if( sig_coeff_flag[ xC ][ yC ] )     inferSbDcSigCoeffFlag= 0   }   if( sig_coeff_flag[ xC ][ yC ] ) {    coeff_sign_flag[ n ]ae(v)    abs_level_gt1_flag[ n ][ 0 ] ae(v)    if( abs_level_gtX_flag[ n][ 0 ] )     par_level_flag[ n ] ae(v)   }   AbsLevelPassX[ xC ][ yC ] =    sig_coeff_flag[ xC ][ yC ] + par_level_flag[ n ] +abs_level_gtX_flag[ n ][ 0 ]  }  /* Greater than X scan passes(numGtXFlags=5) */  for( i = 1; i <= numGtXFlags − 1 &&abs_level_gtX_flag[ n ][ i − 1 ] ; i++ ) {   for( n = numSbCoeff − 1;n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]   abs_level_gtX_flag[ n ][ i ] ae(v)    AbsLevelPassX[ xC ][ yC ] + =2 * abs_level_gtX_flag[ n ][ i ]   }  }  /* remainder scan pass */  for(n = numSbCoeff − 1; n >= 0; n− − ) {   xC = ( xS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]   yC = ( yS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]   if(abs_level_gtX_flag[ n ][ numGtXFlags − 1 ] )    abs_remainder[ n ] ae(v)  TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 − 2 *coeff_sign_flag[ n ] ) *           ( AbsLevelPassX[ xC ][ yC ] +abs_remainder[ n ] )  }  } }

As illustrated in Table 1, according to the VVC standard, beforeencoding/decoding a residual signal (i.e., residual information),whether a transform is applied to a corresponding block may betransmitted first. That is, before residual information on a currentblock is parsed, a transform skip flag (i.e., transform_skip_flag)indicating whether a transform is applied may be parsed first. Thetransform skip flag may be referred to as a transform flag or atransform application flag.

Data is compacted by expressing a correlation between residual signalsin a transformation domain and is transmitted to the decoding apparatus.However, when there is a low correlation between residual signals, datacompaction may not be sufficiently achieved. In this case, a residualsignal in a pixel domain (spatial domain) may be transmitted to thedecoding apparatus while omitting a transform process entailing acomplicated calculation process. Since the residual signal in the pixeldomain, to which no transform is applied, has different characteristics(e.g., the distribution of residual signals, the absolute level of eachresidual signal, and the like) from a residual signal in a generaltransform domain, a residual signal encoding/decoding for efficientlytransmitting the foregoing signal to a decoder is proposed.

FIG. 6 illustrates a decoding apparatus for performing a proposed methodfor transmitting a residual signal in a pixel domain.

A transform skip flag may be transmitted by a unit of a transform block.Referring to Table 1 illustrated above, the transform skip flag may beparsed with respect to a limited specific block size. That is, referringto Table 1, the transform skip flag may be parsed only for a transformblock having a block size equal to or less than a specific size. Forexample, when the size of a current transform block is a 4×4 size orless, the transform skip flag for the current transform block may beparsed.

In one example, the present disclosure proposes an embodiment ofconfiguring various block sizes for determining whether to parse atransform skip flag. Specifically, Log 2TbWidth and log 2TbHeight may bedetermined on variables wN and hN, and according to an existing scheme,the wN and hN may be selected from one of the following.

wN={2, 3, 4, 5, 6}

hN={2, 3, 4, 5, 6}

That is, wN may be one selected from among 2, 3, 4, 5, and 6, and hN maybe one selected from among 2, 3, 4, 5, and 6.

A method of parsing a transform skip flag according to the presentembodiment may be expressed as shown in the following table.

TABLE 15  if( transform_skip_enabled_flag && ( cIdx ! = 0 ||cu_mts_flag[ x0 ][ y0 ] = = 0 ) &&   ( log2TbWidth <= wN ) && (log2TbHeight <= hN ) )   transform_skip_flag[ x0 ][ y0 ][ cIdx ] ae(v)

According to the present embodiment disclosed in Table 15, when log2TbWidth denoting the width of a current block (i.e., a currenttransform block) is wN or less and log 2TbHeight denoting the height ofthe current block is hN or less, a transform skip flag for the currentblock may be parsed. A method of decoding a residual signal of thecurrent block may be determined based on the transform skip flag.According to the proposed embodiment, signals having differentstatistical characteristics may be efficiently processed, therebyreducing the complexity of an entropy decoding process and improvingencoding efficiency.

Alternatively, referring to Table 1, an embodiment in which thetransform skip flag is parsed with respect to a limited specific blocksize but a condition for determining whether to parse the transform skipflag is defined as the number of samples of the block rather than thewidth and height of the block may be proposed. That is, for example, amethod of using the product of log 2TbWidth and log 2TbHeight as acondition for determining whether to parse the syntax elementtransform_skip_flag of the transform skip flag may be proposed.

log 2TbWidth and log 2TbHeight may be selected from among the following.

log 2TbWidth={1, 2, 3, 4, 5, 6}

log 2TbHeight={1, 2, 3, 4, 5, 6}

That is, log 2TbWidth may be one selected from among 1, 2, 3, 4, 5, and6, and log 2TbHeight may be one selected from among 1, 2, 3, 4, 5, and6.

FIG. 7A and FIG. 7B illustrate an embodiment of determining whether toparse a transform skip flag based on the number of samples of a currentblock and a decoding apparatus performing the embodiment.

Referring to FIG. 7A, the decoding apparatus may determine whether it isallowed to determine whether to skip transformation of a current blockper in a high-level syntax (S700). When it is allowed to determinewhether to skip the transformation of the current block in thehigh-level syntax, the decoding apparatus may determine whether thevalue of a syntax element cu_mts_flag is 0 (S710).

When the value of cu_mts_flag is 0, the decoding apparatus may determinewhether the product of log 2TbWidth and log 2TbHeight of the currentblock is a threshold or less (S720). That is, the decoding apparatus maydetermine whether the number of samples of the current block is thethreshold or less.

When the product of log 2TbWidth and log 2TbHeight is the threshold orless, the decoding apparatus may parse the value of a syntax elementtransform_skip_flag of a transform skip flag as 1 (S730).

When the conditions of S700 to S720 are not satisfied, the decodingapparatus may derive the value of the syntax element transform_skip_flagof the transform skip flag as 0 (S740).

FIG. 7B illustrates the decoding apparatus performing an embodiment ofdetermining whether to transform a block using the number of samples inthe block. Referring to FIG. 7B, the decoding apparatus may determinewhether to parse a transform skip flag for the block based on whether atransform skip is allowed in a high-level syntax, block sizeinformation, and whether an MTS is applied.

When determining whether to perform a transform based on the number ofsamples in a block, blocks having various shapes may be included asnon-transform blocks compared to controlling whether to perform atransform based on the width and the height of a block. For example,when both log 2TbWidth and log 2TbHeight are defined as 2 in theforegoing embodiment of controlling whether to perform a transform usingthe width and height of the block, only a 2×4 block, a 4×2 block, and a4×4 block may be included as non-transform blocks. However, when whetherto perform a transform is controlled based on the number of samples, a2×8 block and an 8×2 block may also be included as non-transform blocks.

A method of decoding a residual signal may be determined based on thetransform skip flag. According to the proposed embodiment, signalshaving different statistical characteristics may be efficientlyprocessed, thereby reducing the complexity of an entropy decodingprocess and improving encoding efficiency

For example, an embodiment of encoding/decoding a residual signal for acurrent block in view of statistical characteristics in a case where notransform is applied to the residual signal may be proposed as follows.

Generally, a transform block that is transformed and quantized (i.e.,transform coefficients that are transformed and quantized) has energyconcentrated to a top-left portion of the transform block by thetransformation and decreases in energy level toward the bottom rightportion (high-frequency region) by the quantization. In view of thesecharacteristics, a diagonal scanning technique is introduced as shown inFIG. 5 for efficient residual encoding. However, in a transform skipblock, that is, a transform block including residual coefficients towhich no transform is applied, energy may be evenly distributedthroughout the block rather than being concentrated to the top-leftportion and also has a random level. Therefore, it may be inefficient touse the diagonal scanning technique for encoding. Accordingly, thepresent embodiment proposes a residual scanning method suitable for thecharacteristics of the transform skip block. Here, the residualcoefficients may refer to transform coefficients.

According to another characteristic of the transform skip block, when aprediction mode applied to the transform skip block to be currentlyencoded is an intra prediction mode, the size of a residual sampleincreases to the bottom right portion in which the distance between aprediction sample and a reference sample is large. In view of thischaracteristic, the present embodiment proposes a method in whichresidual signals are rearranged and encoded such that scanning can beperformed from the top left portion of the transform block and adecoding apparatus parses the residual signals and rearranges theresidual signals back to the original positions thereof. That is, thepresent embodiment proposes a method in which residual signals arerearranged and encoded such that a residual signal having a large sizecan be scanned from the top left portion of the transform block and adecoding apparatus parses the residual signals and rearranges theresidual signals back to the original positions thereof. As a similarmethod, a method of defining a new scanning method in a process ofencoding and decoding a residual signal may be considered. However, theresidual rearrangement method proposed in the present embodiment makesit possible to use an existing residual encoding module withoutmodification.

When rearranging residuals while maintaining the existing residualencoding module, a scan order from the top-left region to thebottom-right region needs to be defined.

As one illustrative rearrangement method, a method of rotating a currentblock by 180 degrees may be defined.

FIG. 8 illustrates residual coefficients of a current block to which arearrangement method of 180-degree rotation is applied.

Numbers in the current block illustrated in FIG. 8 denote pixelpositions in the block in a raster scan order. Referring to FIG. 8, aresidual coefficient at the top-left position may be rearranged at thebottom-right position, which is a 180-degree-rotated position. Referringto FIG. 8, the residual coefficients may be rearranged at positionssymmetrical with respect to the center of the transform block throughthe rearrangement method of 180-degree rotation. After therearrangement, a general residual coefficient scan order is applied, anddue to the rearrangement, the residual coefficient at the bottom-leftposition may be considered first and a residual coefficient at thetop-left position may be scanned later.

As another illustrative rearrangement method, a method of mirroring acurrent block may be defined. Mirroring may be classified intoantidiagonal mirroring and main diagonal mirroring depending on amirroring direction.

FIG. 9 illustrates residual coefficients of a current block to which arearrangement method of mirroring is applied. (a) of FIG. 9 illustratesan example of rearranging the residual coefficients of the current blockby antidiagonal mirroring, and (b) of FIG. 9 illustrates an example ofrearranging the residual coefficients of the current block by maindiagonal mirroring.

Referring to (a) of FIG. 9, the residual coefficients may be rearrangedat positions symmetrical with respect to a right upward diagonal of thecurrent block through a rearrangement process using antidiagonalmirroring. Here, the right upward diagonal may refer to a diagonal in aright upward direction passing through the center of the current block.For example, a residual coefficient at the top-left position may berearranged at an antidiagonally mirrored position, which is thebottom-right position. Further, for example, residual coefficient 1(i.e., a residual coefficient neighboring on the right of the residualcoefficient at the top-left position) may be rearranged at anantidiagonally mirrored position, which is a position that is above thebottom-right position. That is, when the width and height of the currentblock are 4, and the top-left sample position of the current block hasan x component of 0 and a y component of 0, a residual coefficient at aposition (1, 0) may be rearranged at an antidiagonally mirroredposition, which is a position (3, 3).

Referring to (b) of FIG. 9, the residual coefficients may be rearrangedat positions symmetrical with respect to a left upward diagonal of thecurrent block through a rearrangement process using main diagonalmirroring. Here, the left upward diagonal may refer to a diagonal in aleft upward direction passing through the center of the current block.For example, a residual coefficient at the top-right position may berearranged at a main-diagonally mirrored position, which is thebottom-left position. Further, for example, residual coefficient 1(i.e., a residual coefficient neighboring on the right of the residualcoefficient at the top-left position) may be rearranged at amain-diagonally mirrored position, which is a position that is below thetop-left position. That is, when the width and height of the currentblock are 4, and the top-left sample position of the current block hasan x component of 0 and a y component of 0, a residual coefficient at aposition (1, 0) may be rearranged at an main-diagonally mirroredposition, which is a position (0, 1).

Alternatively, as another illustrative rearrangement method, a method offlipping a current block may be defined. Flipping may be classified intovertical flipping and horizontal flipping according to a dereferenceaxis.

FIG. 10 illustrates residual coefficients of a current block to which arearrangement method of flipping is applied. (a) of FIG. 10 illustratesan example of rearranging the residual coefficients of the current blockby vertical flipping, and (b) of FIG. 10 illustrates an example ofrearranging the residual coefficients of the current block by horizontalflipping.

Referring to (a) of FIG. 10, the residual coefficients may be rearrangedat positions symmetrical with respect to a vertical axis of the currentblock through a rearrangement process using vertical flipping. Here, thevertical axis may refer to a vertical line passing through the center ofthe current block. For example, a residual coefficient at the top-leftposition may be rearranged at a vertically flipped position, which isthe top-right position. Further, for example, residual coefficient 1(i.e., a residual coefficient neighboring on the right of the residualcoefficient at the top-left position) may be rearranged at a verticallyflipped position, which is a position neighboring on the left of thetop-right position. That is, when the width and height of the currentblock are 4, and the top-left sample position of the current block hasan x component of 0 and a y component of 0, a residual coefficient at aposition (1, 0) may be rearranged at a vertically flipped position,which is a position (2, 0).

Referring to (b) of FIG. 10, the residual coefficients may be rearrangedat positions symmetrical with respect to a horizontal axis of thecurrent block through a rearrangement process using horizontal flipping.Here, the horizontal axis may refer to a horizontal line passing throughthe center of the current block. For example, a residual coefficient atthe top-right position may be rearranged at a horizontally flippedposition, which is the bottom-right position. Further, for example,residual coefficient 1 (i.e., a residual coefficient neighboring on theright of the residual coefficient at the top-left position) may berearranged at a horizontally flipped position, which is a positionneighboring on the right of the bottom-left position. That is, when thewidth and height of the current block are 4, and the top-left sampleposition of the current block has an x component of 0 and a y componentof 0, a residual coefficient at a position (1, 0) may be rearranged at ahorizontally flipped position, which is a position (1, 3).

Alternatively, as another illustrative rearrangement method, a method ofrearranging residual coefficients of a current block according to thedistance to a reference sample of intra prediction may be proposed. Forexample, layers may be defined in a TU according to the distance betweena reference sample and a prediction block, and an encoding apparatus maydetermine whether to perform a transverse-first scan or alongitudinal-first scan on residual coefficients in each layer and maythen rearrange the residual coefficients in an inverse raster order(from right to left and from bottom to top) according to the scan order.That is, layers of the current block may be defined based on thedistance to a reference sample, and the encoding apparatus/decodingapparatus may determine an order in which residual coefficients in eachlayer are scanned as the transverse-first scan or the longitudinal-firstscan and may rearrange the residual coefficients in the inverse rasterorder (from right to left and from bottom to top) according to the scanorder. The decoding apparatus may derive the original residualcoefficients by performing the foregoing rearrangement process inreverse order.

FIG. 11 illustrates residual coefficients of a current block to whichthe foregoing embodiment of dividing layers based on the distance to areference sample and performing rearrangement at positions according toan inverse raster order is applied. (a) of FIG. 11 illustrates anexample in which residual coefficients in each layer are rearranged in atransverse-first scan order at positions according to the inverse rasterorder, and (b) of FIG. 11 illustrates an example in which residualcoefficients in each layer are rearranged in a longitudinal-first scanorder at the positions according to the inverse raster order.

Referring to FIG. 11, layers of the current block may include a firstlayer adjacent to at least one reference sample, a second layer fromwhich the distance to the closest reference sample is 1, a third layerfrom which the distance to the closest reference sample is 2, and afourth layer from which the distance to the closest reference sample is4. That is, the first layer may include residual coefficients (e.g.,residual coefficients 0 to 4, residual coefficient 8, and residualcoefficient 12 of the current block before rearrangement illustrated inFIG. 11) adjacent to the at least one reference sample (i.e., the firstlayer may include residual coefficients from which the distance to theclosest reference sample is 1), the second layer may include residualcoefficients (e.g., residual coefficients 5 to 7, residual coefficient9, and residual coefficient 13 of the current block before rearrangementillustrated in FIG. 11) from which the distance to the closest referencesample is 2, the third layer may include residual coefficients (e.g.,residual coefficients 10, 11, and 14 of the current block beforerearrangement illustrated in FIG. 11) from which the distance to theclosest reference sample is 3, and the fourth layer may include aresidual coefficient (e.g., residual coefficient 15 of the current blockbefore rearrangement illustrated in FIG. 11) from which the distance tothe closest reference sample is 4.

When the layers of the current block are defined as described above, anencoding apparatus may determine one of a transverse-first scan and alongitudinal-first scan as a scan method for the layers of the currentblock.

For example, when the transverse-first scan is determined as the scanmethod for the layers of the current block, the residual coefficientsmay be rearranged as shown in (a) of FIG. 11.

Specifically, the encoding apparatus may perform scanning in an orderfrom the first layer to the fourth layer, in which case the encodingapparatus may scan transverse residual coefficients in each layer from aresidual coefficient at the top-left position, and may scan theremaining longitudinal residual coefficients from top to bottom afterscanning all of the transverse residual coefficients.

For example, transverse residual coefficients in the first layer mayinclude residual coefficients 0 to 3, and longitudinal residualcoefficients in the first layer may include residual coefficients 4, 8,and 12. The encoding apparatus/decoding apparatus may scan thetransverse residual coefficients in the first layer in a left-to-rightorder (scan residual coefficients 0, 1, 2, and 3 in order) and may thenscan the longitudinal residual coefficients in the first layer in atop-to-bottom order (scans residual coefficients 4, 8, and 12 in order).Next, the second layer may be scanned. Transverse residual coefficientsin the second layer may include residual coefficients 5 to 7, andlongitudinal residual coefficients in the second layer may includeresidual coefficients 9 and 13. The encoding apparatus may scan thetransverse residual coefficients in the second layer in theleft-to-right order (scan residual coefficients 5, 6, and 7 in order)and may then scan the longitudinal residual coefficients in the secondlayer in the top-to-bottom order (scans residual coefficients 9 and 13in order). Next, the third layer may be scanned. Transverse residualcoefficients in the third layer may include residual coefficients 10 and11, and a longitudinal residual coefficient in the third layer mayinclude residual coefficient 14. The encoding apparatus may scan thetransverse residual coefficients in the third layer in the left-to-rightorder (scan residual coefficients 10 and 11 in order) and may then scanthe longitudinal residual coefficients in the third layer in thetop-to-bottom order (scans residual coefficient 14). Next, the fourthlayer may be scanned. A transverse residual coefficient in the fourthlayer may include residual coefficient 15. The encoding apparatus mayscan the transverse residual coefficient in the fourth layer in theleft-to-right order (scan residual coefficient 15).

Subsequently, referring to (a) of FIG. 11, the encoding apparatus mayrearrange the residual coefficients in the scan order at positionsaccording to the inverse raster order (from right to left and frombottom to top). As described above, the scan order of the residualcoefficients is an order of residual coefficients 0, 1, 2, 3, 4, 8, 12,5, 6, 7, 9, 13, 10, 11, 14, and 15. The residual coefficients may berearranged in the scan order at the positions according to the inverseraster order in the current block. For example, residual coefficient 0may be rearranged at the bottom-right position, residual coefficients 1,2, and 3 may be rearranged in a left direction of the bottom-rightposition, residual coefficients 4, 8, 12, and 5 may be rearranged in aright-to-left order in an upper row (i.e., a third row of the currentblock) of the bottom-right position, residual coefficients 6, 7, 9, and13 may be rearranged in the right-to-left order in a second row of thecurrent block, and residual coefficients 10, 11, 14, and 15 may berearranged in the right-to-left order in a first row of the currentblock.

Further, for example, when the longitudinal-first scan is determined asthe scan method for the layers of the current block, the residualcoefficients may be rearranged as shown in (b) of FIG. 11.

Specifically, the encoding apparatus may perform scanning in an orderfrom the first layer to the fourth layer, in which case the encodingapparatus may scan longitudinal residual coefficients in each layer fromthe residual coefficient at the top-left position, and may scan theremaining transverse residual coefficients from top to bottom afterscanning all of the longitudinal residual coefficients.

For example, longitudinal residual coefficients in the first layer mayinclude residual coefficients 0, 4, 8, and 12, and transverse residualcoefficients in the first layer may include residual coefficients 1 to3. The encoding apparatus may scan the longitudinal residualcoefficients in the first layer in the top-to-bottom order (scanresidual coefficients 0, 4, 8, and 12 in order) and may then scan thetransverse residual coefficients in the first layer in the left-to-rightorder (scans residual coefficients 1, 2, and 3 in order). Next, thesecond layer may be scanned. Longitudinal residual coefficients in thesecond layer may include residual coefficients 5, 9, and 13, andtransverse residual coefficients in the second layer may includeresidual coefficients 6 and 7. The encoding apparatus may scan thelongitudinal residual coefficients in the second layer in thetop-to-bottom order (scan residual coefficients 5, 9, and 13 in order)and may then scan the transverse residual coefficients in the secondlayer in the left-to-right order (scans residual coefficients 6 and 6 inorder). Next, the third layer may be scanned. Longitudinal residualcoefficients in the third layer may include residual coefficients 10 and14, and a transverse residual coefficient in the third layer may includeresidual coefficient 11. The encoding apparatus may scan thelongitudinal residual coefficients in the third layer in thetop-to-bottom order (scan residual coefficients 10 and 14 in order) andmay then scan the transverse residual coefficients in the third layer inthe left-to-right order (scans residual coefficient 11). Next, thefourth layer may be scanned. A longitudinal residual coefficient in thefourth layer may include residual coefficient 15. The encoding apparatusmay scan the longitudinal residual coefficient in the fourth layer inthe top-to-bottom order (scan residual coefficient 15).

Subsequently, referring to (b) of FIG. 11, the encoding apparatus mayrearrange the residual coefficients in the scan order at positionsaccording to the inverse raster order (from right to left and frombottom to top). As described above, the scan order of the residualcoefficients is an order of residual coefficients 0, 4, 8, 12, 1, 2, 3,5, 9, 13, 6, 7, 10, 14, 11, and 15. The residual coefficients may berearranged in the scan order at the positions according to the inverseraster order in the current block. For example, residual coefficient 0may be rearranged at the bottom-right position, residual coefficients 4,8, and 12 may be rearranged in the left direction of the bottom-rightposition, residual coefficients 1, 2, 3, and 5 may be rearranged in theright-to-left order in the upper row (i.e., the third row of the currentblock) of the bottom-right position, residual coefficients 9, 13, 6, and7 may be rearranged in the right-to-left order in the second row of thecurrent block, and residual coefficients 10, 14, 11, and 15 may berearranged in the right-to-left order in the first row of the currentblock.

Alternatively, another embodiment of rearranging residual coefficientsof a current block according to the distance to a reference sample ofintra prediction may be proposed. For example, layers may be defined ina TU according to the distance between a reference sample and aprediction block, and an encoding apparatus may determine whether toperform a transverse-first scan or a longitudinal-first scan on residualcoefficients in each layer and may then rearrange the residualcoefficients in an diagonal scan order according to the scan order. Thatis, layers of the current block may be defined based on the distance toa reference sample, and the encoding apparatus may determine an order inwhich residual coefficients in each layer are scanned as thetransverse-first scan or the longitudinal-first scan and may rearrangethe residual coefficients according to the scan order at positionsaccording to the diagonal scan order. A decoding apparatus may derivethe original residual coefficients by performing the foregoingrearrangement process in reverse order.

FIG. 12 illustrates residual coefficients of a current block to whichthe foregoing embodiment of dividing layers based on the distance to areference sample and performing rearrangement at positions according toa diagonal scan order is applied. (a) of FIG. 12 illustrates an examplein which residual coefficients in each layer are rearranged in atransverse-first scan order at positions according to the diagonal scanorder, and (b) of FIG. 12 illustrates an example in which residualcoefficients in each layer are rearranged in a longitudinal-first scanorder at the positions according to the diagonal scan order.

Referring to FIG. 12, layers of the current block may include a firstlayer adjacent to at least one reference sample, a second layer fromwhich the distance to the closest reference sample is 1, a third layerfrom which the distance to the closest reference sample is 2, and afourth layer from which the distance to the closest reference sample is4. That is, the first layer may include residual coefficients (e.g.,residual coefficients 0 to 4, residual coefficient 8, and residualcoefficient 12 of the current block before rearrangement illustrated inFIG. 12) adjacent to the at least one reference sample (i.e., the firstlayer may include residual coefficients from which the distance to theclosest reference sample is 1), the second layer may include residualcoefficients (e.g., residual coefficients 5 to 7, residual coefficient9, and residual coefficient 13 of the current block before rearrangementillustrated in FIG. 12) from which the distance to the closest referencesample is 2, the third layer may include residual coefficients (e.g.,residual coefficients 10, 11, and 14 of the current block beforerearrangement illustrated in FIG. 12) from which the distance to theclosest reference sample is 3, and the fourth layer may include aresidual coefficient (e.g., residual coefficient 15 of the current blockbefore rearrangement illustrated in FIG. 12) from which the distance tothe closest reference sample is 4.

When the layers of the current block are defined as described above, anencoding apparatus may determine one of a transverse-first scan and alongitudinal-first scan as a scan method for the layers of the currentblock.

For example, when the transverse-first scan is determined as the scanmethod for the layers of the current block, the residual coefficientsmay be rearranged as shown in (a) of FIG. 12.

Specifically, the encoding apparatus may perform scanning in an orderfrom the first layer to the fourth layer, in which case the encodingapparatus may scan transverse residual coefficients in each layer from aresidual coefficient at the top-left position, and may scan theremaining longitudinal residual coefficients from top to bottom afterscanning all of the transverse residual coefficients.

For example, transverse residual coefficients in the first layer mayinclude residual coefficients 0 to 3, and longitudinal residualcoefficients in the first layer may include residual coefficients 4, 8,and 12. The encoding apparatus may scan the transverse residualcoefficients in the first layer in a left-to-right order (scan residualcoefficients 0, 1, 2, and 3 in order) and may then scan the longitudinalresidual coefficients in the first layer in a top-to-bottom order (scansresidual coefficients 4, 8, and 12 in order). Next, the second layer maybe scanned. Transverse residual coefficients in the second layer mayinclude residual coefficients 5 to 7, and longitudinal residualcoefficients in the second layer may include residual coefficients 9 and13. The encoding apparatus may scan the transverse residual coefficientsin the second layer in the left-to-right order (scan residualcoefficients 5, 6, and 7 in order) and may then scan the longitudinalresidual coefficients in the second layer in the top-to-bottom order(scans residual coefficients 9 and 13 in order). Next, the third layermay be scanned. Transverse residual coefficients in the third layer mayinclude residual coefficients 10 and 11, and a longitudinal residualcoefficient in the third layer may include residual coefficient 14. Theencoding apparatus may scan the transverse residual coefficients in thethird layer in the left-to-right order (scan residual coefficients 10and 11 in order) and may then scan the longitudinal residualcoefficients in the third layer in the top-to-bottom order (scansresidual coefficient 14). Next, the fourth layer may be scanned. Atransverse residual coefficient in the fourth layer may include residualcoefficient 15. The encoding apparatus may scan the transverse residualcoefficient in the fourth layer in the left-to-right order (scanresidual coefficient 15).

Subsequently, referring to (a) of FIG. 12, the encoding apparatus mayrearrange the residual coefficients in the scan order at positionsaccording to the diagonal scan order (from top-right to bottom-left andfrom bottom-right to top-left). As described above, the scan order ofthe residual coefficients is an order of residual coefficients 0, 1, 2,3, 4, 8, 12, 5, 6, 7, 9, 13, 10, 11, 14, and 15. The residualcoefficients may be rearranged in the scan order at the positionsaccording to the diagonal scan order in the current block. For example,residual coefficient 0 may be rearranged at the bottom-right position ona first right upward diagonal, residual coefficients 1 and 2 may berearranged in an upper right-to-lower left order on a second rightupward diagonal (i.e., a right upward diagonal on the upper left of thefirst right upward diagonal) of the current block, residual coefficients3, 4, and 8 may be rearranged in the upper right-to-lower left order ona third right upward diagonal (i.e., a right upward diagonal on theupper left of the second right upward diagonal) of the current block,residual coefficients 12, 5, 6, and 7 may be rearranged in the upperright-to-lower left order on a fourth right upward diagonal (i.e., aright upward diagonal on the upper left of the third right upwarddiagonal) of the current block, residual coefficients 9, 13, and 10 maybe rearranged in the upper right-to-lower left order on a fifth rightupward diagonal (i.e., a right upward diagonal on the upper left of thefourth right upward diagonal) of the current block, residualcoefficients 11 and 14 may be rearranged in the upper right-to-lowerleft order on a sixth right upward diagonal (i.e., a right upwarddiagonal on the upper left of the fifth right upward diagonal) of thecurrent block, and residual coefficient 15 may be rearranged in theupper right-to-lower left order on a seventh right upward diagonal(i.e., a right upward diagonal on the upper left of the sixth rightupward diagonal) of the current block.

Further, for example, when the longitudinal-first scan is determined asthe scan method for the layers of the current block, the residualcoefficients may be rearranged as shown in (b) of FIG. 12.

Specifically, the encoding apparatus may perform scanning in an orderfrom the first layer to the fourth layer, in which case the encodingapparatus may scan longitudinal residual coefficients in each layer fromthe residual coefficient at the top-left position, and may scan theremaining transverse residual coefficients from top to bottom afterscanning all of the longitudinal residual coefficients.

For example, longitudinal residual coefficients in the first layer mayinclude residual coefficients 0, 4, 8, and 12, and transverse residualcoefficients in the first layer may include residual coefficients 1 to3. The encoding apparatus may scan the longitudinal residualcoefficients in the first layer in the top-to-bottom order (scanresidual coefficients 0, 4, 8, and 12 in order) and may then scan thetransverse residual coefficients in the first layer in the left-to-rightorder (scans residual coefficients 1, 2, and 3 in order). Next, thesecond layer may be scanned. Longitudinal residual coefficients in thesecond layer may include residual coefficients 5, 9, and 13, andtransverse residual coefficients in the second layer may includeresidual coefficients 6 and 7. The encoding apparatus may scan thelongitudinal residual coefficients in the second layer in thetop-to-bottom order (scan residual coefficients 5, 9, and 13 in order)and may then scan the transverse residual coefficients in the secondlayer in the left-to-right order (scans residual coefficients 6 and 6 inorder). Next, the third layer may be scanned. Longitudinal residualcoefficients in the third layer may include residual coefficients 10 and14, and a transverse residual coefficient in the third layer may includeresidual coefficient 11. The encoding apparatus may scan thelongitudinal residual coefficients in the third layer in thetop-to-bottom order (scan residual coefficients 10 and 14 in order) andmay then scan the transverse residual coefficients in the third layer inthe left-to-right order (scans residual coefficient 11). Next, thefourth layer may be scanned. A longitudinal residual coefficient in thefourth layer may include residual coefficient 15. The encoding apparatusmay scan the longitudinal residual coefficient in the fourth layer inthe top-to-bottom order (scan residual coefficient 15).

Subsequently, referring to (b) of FIG. 12, the encoding apparatus mayrearrange the residual coefficients in the scan order at positionsaccording to the diagonal scan order (from top-right to bottom-left andfrom bottom-right to top-left). As described above, the scan order ofthe residual coefficients is an order of residual coefficients 0, 4, 8,12, 1, 2, 3, 5, 9, 13, 6, 7, 10, 14, 11, and 15. The residualcoefficients may be rearranged in the scan order at the positionsaccording to the diagonal scan order in the current block. For example,residual coefficient 0 may be rearranged at the bottom-right position onthe first right upward diagonal, residual coefficients 4 and 8 may berearranged in the upper right-to-lower left order on the second rightupward diagonal (i.e., the right upward diagonal on the upper left ofthe first right upward diagonal) of the current block, residualcoefficients 12, 1, 28 may be rearranged in the upper right-to-lowerleft order on the third right upward diagonal (i.e., the right upwarddiagonal on the upper left of the second right upward diagonal) of thecurrent block, residual coefficients 3, 5, 9, and 13 may be rearrangedin the upper right-to-lower left order on the fourth right upwarddiagonal (i.e., the right upward diagonal on the upper left of the thirdright upward diagonal) of the current block, residual coefficients 6, 7,and 10 may be rearranged in the upper right-to-lower left order on thefifth right upward diagonal (i.e., the right upward diagonal on theupper left of the fourth right upward diagonal) of the current block,residual coefficients 14 and 11 may be rearranged in the upperright-to-lower left order on the sixth right upward diagonal (i.e., theright upward diagonal on the upper left of the fifth right upwarddiagonal) of the current block, and residual coefficient 15 may berearranged in the upper right-to-lower left order on the seventh rightupward diagonal (i.e., the right upward diagonal on the upper left ofthe sixth right upward diagonal) of the current block.

Alternatively, another embodiment of rearranging residual coefficientsof a current block according to the distance to a reference sample ofintra prediction may be proposed. For example, a method of setting areference sample (left reference sample or upper reference sample)serving as a reference, scanning residual coefficients by defininglayers of a current block based on the distance to the set referencesample, and rearranging the residual coefficients in the scan order atpositions according to a diagonal scan order may be proposed. Here, theresidual coefficients in the layers defined based on the distance to theleft reference sample may be scanned by a longitudinal-first scan, andthe residual coefficients in the layers defined based on the distance tothe upper reference sample may be scanned by a transverse-first scan.

FIG. 13 illustrates residual coefficients of a current block to whichthe foregoing embodiment of dividing layers based on the distance to aspecific reference sample and performing rearrangement at positionsaccording to a diagonal scan order is applied. (a) of FIG. 13illustrates an example in which residual coefficients in layersconfigured based on the distance to an upper reference sample arerearranged in a transverse-first scan order at positions according tothe diagonal scan order, and (b) of FIG. 13 illustrates an example inwhich residual coefficients in layers configured based on the distanceto a left reference sample are rearranged in a longitudinal-first scanorder at the positions according to the diagonal scan order. A decodingdevice may derive the original residual coefficient by performing theforegoing rearrangement process in reverse order.

Referring to (a) of FIG. 13, layers of the current block may include afirst layer adjacent to at least one upper reference sample, a secondlayer from which the distance to the closest upper reference sample is1, a third layer from which the distance to the closest upper referencesample is 2, and a fourth layer from which the distance to the closestupper reference sample is 4. That is, the first layer may includeresidual coefficients (e.g., residual coefficients 0 to 3 of the currentblock before rearrangement illustrated in (a) of FIG. 13) adjacent tothe at least one upper reference sample (i.e., the first layer mayinclude residual coefficients from which the distance to the closestupper reference sample is 1), the second layer may include residualcoefficients (e.g., residual coefficients 4 to 7 of the current blockbefore rearrangement illustrated in (a) of FIG. 13) from which thedistance to the closest upper reference sample is 2, the third layer mayinclude residual coefficients (e.g., residual coefficients 8 to 11 ofthe current block before rearrangement illustrated in (a) of FIG. 13)from which the distance to the closest upper reference sample is 3, andthe fourth layer may include residual coefficients (e.g., residualcoefficients 12 to 15 of the current block before rearrangementillustrated in (a) of FIG. 13) from which the distance to the closestupper reference sample is 4. That is, the first layer may derive from afirst row of the current block, the second layer from a second row ofthe current block, the third layer from a third row of the currentblock, and the fourth layer from a fourth row of the current block.

When the layers of the current block are defined as described above, anencoding apparatus may determine a transverse-first scan as a scanmethod for the layers of the current block. Subsequently, the residualcoefficients may be rearranged as shown in (a) of FIG. 13.

Specifically, the encoding apparatus may perform scanning in an orderfrom the first layer to the fourth layer, and may scan residualcoefficient in each layer from left to right.

For example, the encoding apparatus may scan the residual coefficientsin the first layer in a left-to-right order (scan residual coefficients0, 1, 2, and 3 in order). Next, the second layer may be scanned. Theencoding apparatus may scan the residual coefficients in the secondlayer in the left-to-right order (scan residual coefficients 4, 5, 6,and 7 in order). Next, the third layer may be scanned. The encodingapparatus may scan the residual coefficients in the third layer in theleft-to-right order (scan residual coefficients 8, 9, 10, and 11 inorder). Next, the fourth layer may be scanned. The encoding apparatusmay scan the residual coefficients in the fourth layer in theleft-to-right order (scan residual coefficients 12, 13, 14, and 15 inorder).

Subsequently, referring to (a) of FIG. 13, the encoding apparatus mayrearrange the residual coefficients in the scan order at positionsaccording to the diagonal scan order (from top-right to bottom-left andfrom bottom-right to top-left). As described above, the scan order ofthe residual coefficients is an order of residual coefficients 0, 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15. The residualcoefficients may be rearranged in the scan order at the positionsaccording to the diagonal scan order in the current block. For example,residual coefficient 0 may be rearranged at the bottom-right position ona first right upward diagonal, residual coefficients 1 and 2 may berearranged in an upper right-to-lower left order on a second rightupward diagonal (i.e., a right upward diagonal on the upper left of thefirst right upward diagonal) of the current block, residual coefficients3, 4, and 5 may be rearranged in the upper right-to-lower left order ona third right upward diagonal (i.e., a right upward diagonal on theupper left of the second right upward diagonal) of the current block,residual coefficients 6, 7, 8, and 9 may be rearranged in the upperright-to-lower left order on a fourth right upward diagonal (i.e., aright upward diagonal on the upper left of the third right upwarddiagonal) of the current block, residual coefficients 10, 11, and 12 maybe rearranged in the upper right-to-lower left order on a fifth rightupward diagonal (i.e., a right upward diagonal on the upper left of thefourth right upward diagonal) of the current block, residualcoefficients 13 and 14 may be rearranged in the upper right-to-lowerleft order on a sixth right upward diagonal (i.e., a right upwarddiagonal on the upper left of the fifth right upward diagonal) of thecurrent block, and residual coefficient 15 may be rearranged in theupper right-to-lower left order on a seventh right upward diagonal(i.e., a right upward diagonal on the upper left of the sixth rightupward diagonal) of the current block.

Referring to (b) of FIG. 13, layers of the current block may include afirst layer adjacent to at least one left reference sample, a secondlayer from which the distance to the closest left reference sample is 1,a third layer from which the distance to the closest left referencesample is 2, and a fourth layer from which the distance to the closestleft reference sample is 4. That is, the first layer may includeresidual coefficients (e.g., residual coefficients 0, 4, 8, and 12 ofthe current block before rearrangement illustrated in (b) of FIG. 13)adjacent to the at least one upper reference sample (i.e., the firstlayer may include residual coefficients from which the distance to theclosest left reference sample is 1), the second layer may includeresidual coefficients (e.g., residual coefficients 1, 5, 9, and 13 ofthe current block before rearrangement illustrated in (b) of FIG. 13)from which the distance to the closest left reference sample is 2, thethird layer may include residual coefficients (e.g., residualcoefficients 2, 6, 10, and 14 of the current block before rearrangementillustrated in (b) of FIG. 13) from which the distance to the closestleft reference sample is 3, and the fourth layer may include residualcoefficients (e.g., residual coefficients 3, 7, 11, and 15 of thecurrent block before rearrangement illustrated in (b) of FIG. 13) fromwhich the distance to the closest left reference sample is 4. That is,the first layer may derive from a first column of the current block, thesecond layer from a second column of the current block, the third layerfrom a third column of the current block, and the fourth layer from afourth column of the current block.

When the layers of the current block are defined as described above, anencoding apparatus may determine a longitudinal-first scan as a scanmethod for the layers of the current block. Subsequently, the residualcoefficients may be rearranged as shown in (b) of FIG. 13.

Specifically, the encoding apparatus may perform scanning in an orderfrom the first layer to the fourth layer, and may scan residualcoefficient in each layer from top to bottom.

For example, the encoding apparatus may scan the residual coefficientsin the first layer in a top-to-bottom order (scan residual coefficients0, 4, 8, and 12 in order). Next, the second layer may be scanned. Theencoding apparatus may scan the residual coefficients in the secondlayer in the top-to-bottom order (scan residual coefficients 1, 5, 9,and 13 in order). Next, the third layer may be scanned. The encodingapparatus may scan the residual coefficients in the third layer in thetop-to-bottom order (scan residual coefficients 2, 6, 10, and 14 inorder). Next, the fourth layer may be scanned. The encoding apparatusmay scan the residual coefficients in the fourth layer in thetop-to-bottom order (scan residual coefficients 3, 7, 11, and 15 inorder).

Subsequently, referring to (b) of FIG. 13, the encoding apparatus mayrearrange the residual coefficients in the scan order at positionsaccording to the diagonal scan order (from top-right to bottom-left andfrom bottom-right to top-left). As described above, the scan order ofthe residual coefficients is an order of residual coefficients 0, 4, 8,12, 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, and 15. The residualcoefficients may be rearranged in the scan order at the positionsaccording to the diagonal scan order in the current block. For example,residual coefficient 0 may be rearranged at the bottom-right position ona first right upward diagonal, residual coefficients 4 and 8 may berearranged in an upper right-to-lower left order on a second rightupward diagonal (i.e., a right upward diagonal on the upper left of thefirst right upward diagonal) of the current block, residual coefficients12, 1, and 5 may be rearranged in the upper right-to-lower left order ona third right upward diagonal (i.e., a right upward diagonal on theupper left of the second right upward diagonal) of the current block,residual coefficients 9, 13, 2, and 6 may be rearranged in the upperright-to-lower left order on a fourth right upward diagonal (i.e., aright upward diagonal on the upper left of the third right upwarddiagonal) of the current block, residual coefficients 10, 14, and 3 maybe rearranged in the upper right-to-lower left order on a fifth rightupward diagonal (i.e., a right upward diagonal on the upper left of thefourth right upward diagonal) of the current block, residualcoefficients 7 and 11 may be rearranged in the upper right-to-lower leftorder on a sixth right upward diagonal (i.e., a right upward diagonal onthe upper left of the fifth right upward diagonal) of the current block,and residual coefficient 15 may be rearranged in the upperright-to-lower left order on a seventh right upward diagonal (i.e., aright upward diagonal on the upper left of the sixth right upwarddiagonal) of the current block.

For example, the foregoing rearrangement methods may be performed whenno transform is applied to the residual coefficients of the currentblock. That is, whether to apply the rearrangement methods may bedetermined based on whether a transform is applied to the residualcoefficients. In other words, whether to apply the rearrangement methodsmay be determined based on a transform skip flag for the current block.

FIG. 14A and FIG. 14B illustrate an embodiment of determining whether toapply a rearrangement method based on a transform skip flag for acurrent block and an encoding apparatus and a decoding apparatusperforming the embodiment.

Referring to FIG. 14A, the encoding apparatus and the decoding apparatusmay determine whether the value of a transform skip flag for a currentblock is 1 (S1400). When the value of the transform skip flag is 1, theencoding apparatus and the decoding apparatus may perform arearrangement method on residual coefficients of the current block(S1410). When the value of the transform skip flag is not 1 (i.e., whenthe value of the transform skip flag is 0), the encoding apparatus andthe decoding apparatus may not perform a rearrangement method on theresidual coefficients of the current block. The transform skip flag mayindicate whether a transform is applied to the residual coefficients ofthe current block. That is, the transform skip flag may indicate whetherthe transform has been applied to the residual coefficients. A syntaxelement indicating the transform skip flag may be transform_skip_flagillustrated above.

FIG. 14B illustrates the encoding apparatus and the decoding apparatusthat determine whether to apply the rearrangement method based on thetransform skip flag for the current block and perform the rearrangementmethod. A residual rearranger of the encoding apparatus may determinewhether to rearrange the residual coefficients based on the transformskip flag for the current block, and may rearrange the residualcoefficients when the value of the transform skip value is 1. Aquantizer and an entropy encoder of the encoding apparatus may performquantization and entropy encoding on the rearranged residualcoefficients to generate residual information and may output the encodedresidual information through a bitstream. An entropy decoder of thedecoding apparatus may receive the bitstream including the residualinformation on the current block and may decode the residual informationto derive the quantized residual coefficients. Subsequently, adequantizer of the decoding apparatus may dequantize (i.e., scale) thequantized residual coefficients, thereby deriving the residualcoefficients. A residual rearranger of the decoding apparatus maydetermine whether to rearrange the residual coefficients based on thetransform skip flag for the current block, and may rearrange theresidual coefficients when the value of the transform skip value is 1.

Alternatively, methods of using the foregoing rearrangement methods incombination under various conditions may be proposed.

In one example, a rearrangement method or whether to performrearrangement may be determined based on the size of the current block.Here, the size of the current block may denote the number of samples ofthe current block or the width and height of the current block. Forexample, when the number of samples of the current block is less than64, a rearrangement method of 180-degree rotation described above may beapplied to the residual coefficients of the current block, and when thenumber of samples of the current block is 64 or greater, a rearrangementmethod of mirroring described above may be applied to the residualcoefficients of the current block. In another example, when the numberof samples of the current block is less than 64, one of therearrangement methods described above may be applied to the residualcoefficients of the current block, and when the number of samples of thecurrent block is 64 or greater, no rearrangement method may be applied.In one example, a process of determining a rearrangement method orwhether to perform rearrangement based on the foregoing condition may beperformed only when the value of the transform skip flag for the currentblock is 1. That is, when the value of the transform skip flag for thecurrent block is 1, a rearrangement method or whether to performrearrangement may be determined based on the size (number of samples orwidth and height) of the current block.

In an alternative example, a rearrangement method or whether to performrearrangement may be determined based on the shape of the current block.For example, when the current block is a square block (i.e., when thewidth and height of the current block are the same), the rearrangementmethod of mirroring may be applied to the residual coefficients of thecurrent block, and when the current block is a non-square block (i.e.,when the width and height of the current block are different), therearrangement method of 180-degree rotation may be applied to theresidual coefficients of the current block. In one example, a process ofdetermining a rearrangement method or whether to perform rearrangementbased on the foregoing condition may be performed only when the value ofthe transform skip flag for the current block is 1. That is, when thevalue of the transform skip flag for the current block is 1, arearrangement method or whether to perform rearrangement may bedetermined based on the shape of the current block.

In an alternative example, a rearrangement method or whether to performrearrangement may be determined based on the ratio of the width of thecurrent block to the height thereof. For example, when the ratio of thewidth of the current block to the height is 2 or greater or is ½ or less(i.e., when a value obtained by dividing the width of the current blockby the height is 2 or greater or is ½ or less), the rearrangement methodof mirroring may be applied to the residual coefficients of the currentblock, and when the ratio of the width of the current block to theheight is less than 2 and is greater than ½ (i.e., the value obtained bydividing the width of the current block by the height is less than 2 andis greater than ½), the rearrangement method of 180-degree rotation maybe applied to the residual coefficients of the current block.Alternatively, for example, when the ratio of the width of the currentblock to the height is 2 or greater or is ½ or less (i.e., when a valueobtained by dividing the width of the current block by the height is 2or greater or is ½ or less), the rearrangement method of mirroring maybe applied to the residual coefficients of the current block, and whenthe ratio of the width of the current block to the height is less than 2and is greater than ½ (i.e., the value obtained by dividing the width ofthe current block by the height is less than 2 and is greater than ½),no rearrangement method may be applied to the residual coefficients ofthe current block. In one example, a process of determining arearrangement method or whether to perform rearrangement based on theforegoing condition may be performed only when the value of thetransform skip flag for the current block is 1. That is, when the valueof the transform skip flag for the current block is 1, a rearrangementmethod or whether to perform rearrangement may be determined based onthe ratio of the width of the current block to the height thereof.

In an alternative example, when intra prediction is applied to thecurrent block, a rearrangement method or whether to performrearrangement may be determined based on an intra prediction mode forthe current block. For example, when the prediction direction of theintra prediction mode for the current block is close to a horizontaldirection or a vertical direction, a left reference sample or an upperreference sample is mainly used for prediction, causing predictionerrors to be concentrated in one reference sample direction, and thus anembodiment of determining a rearrangement method in view of thischaracteristic may be proposed. For example, when the predictiondirection of the intra prediction mode for the current block is thehorizontal direction or the intra prediction mode for the current blockis an intra prediction mode in which a left reference sample is mainlyused for prediction, a rearrangement method of vertical flippingdescribed above may be applied, and when the prediction direction of theintra prediction mode for the current block is the vertical direction orthe intra prediction mode for the current block is an intra predictionmode in which an upper reference sample is mainly used for prediction, arearrangement method of horizontal flipping described above may beapplied. In one example, a process of determining a rearrangement methodor whether to perform rearrangement based on the foregoing condition maybe performed only when the value of the transform skip flag for thecurrent block is 1. That is, when the value of the transform skip flagfor the current block is 1, a rearrangement method or whether to performrearrangement may be determined based on the intra prediction mode forthe current block.

In an alternative example, a rearrangement method or whether to performrearrangement may be determined based on a high-level syntax in thebitstream transmitted from the encoding apparatus. For example, a flagindicating whether to perform rearrangement may be transmitted throughthe high-level syntax, such as a sequence parameter set (SPS) or apicture parameter set (PPS), and whether to perform rearrangement and arearrangement method in a subsyntax referencing the high-level syntaxmay be determined based on the flag. In one example, a process ofdetermining a rearrangement method or whether to perform rearrangementbased on the foregoing condition may be performed only when the value ofthe transform skip flag for the current block is 1. That is, when thevalue of the transform skip flag for the current block is 1, the flagindicating whether to perform rearrangement may be transmitted throughthe high-level syntax, such as the sequence parameter set (SPS) or thepicture parameter set (PPS), and a rearrangement method or whether toperform rearrangement may be determined based on the flag.

In an alternative example, a rearrangement method or whether to performrearrangement may be determined based on a prediction mode for thecurrent block. For example, an embodiment in which a rearrangementmethod is used only for a residual signal of a block predicted in anintra prediction mode without using a residual rearrangement method foran inter prediction mode in which a residual signal is relatively lessgenerated may be proposed. That is, when inter prediction is applied tothe current block, no rearrangement method may be applied to theresidual coefficients of the current block, and when intra prediction isapplied to the current block, the rearrangement method may be applied tothe residual coefficients of the current block. In one example, aprocess of determining a rearrangement method or whether to performrearrangement based on the foregoing condition may be performed onlywhen the value of the transform skip flag for the current block is 1.That is, when the value of the transform skip flag for the current blockis 1, a rearrangement method or whether to perform rearrangement may bedetermined based on the prediction mode for the current block.

In an alternative example, a rearrangement method or whether to performrearrangement may be determined based on whether quantization isapplied. For example, no residual rearrangement method may be performedin lossless decoding in which no quantization is applied, and a residualrearrangement method may be performed in lossy decoding in whichquantization is applied. That is, when no quantization is applied to theresidual coefficients of the current block, no rearrangement method maybe applied to the residual coefficients of the current block, whenquantization is applied to the residual coefficients of the currentblock, the rearrangement method may be applied to the residualcoefficients of the current block. In one example, a process ofdetermining a rearrangement method or whether to perform rearrangementbased on the foregoing condition may be performed only when the value ofthe transform skip flag for the current block is 1. That is, when thevalue of the transform skip flag for the current block is 1, arearrangement method or whether to perform rearrangement may bedetermined based on whether quantization is applied to the residualcoefficients of the current block.

Meanwhile, as described above, since a block which is not subjected totransform encoding, that is, a transform block including residualcoefficients to which no transform is applied, has differentcharacteristics of residual information from those of a block which issubjected to general transform encoding, an efficient residual dataencoding method for a block which is not subjected to transform encodingis necessary.

Accordingly, the present disclosure proposes embodiments ofencoding/decoding residual information for a transform skip block. Here,a transform skip flag indicating whether transform is applied may betransmitted by a unit of a transform block, and the size of a transformblock is not limited in the embodiments of the present disclosure. Forexample, when the value of the transform skip flag is 1, a method ofencoding/decoding residual information proposed in the presentdisclosure may be performed. When the value of the transform skip flagis 0, a method of encoding/decoding existing residual information, suchas syntax elements for residual information illustrated in Table 1, maybe performed.

FIG. 15 illustrates an example of determining a method of codingresidual information based on a transform skip flag.

Referring to FIG. 15, an encoding apparatus may determine whether thevalue of a transform skip flag for a current block is 1 (S1500).

When the value of the transform skip flag is 1, the encoding apparatusmay rearrange residual coefficients of the current block (S1510). Here,as a method for rearranging the residual coefficients, at least one ofthe foregoing embodiments may be used. For example, whether to rearrangethe residual coefficients may be determined based on whether aprediction mode for the current block is an inter prediction mode or anintra prediction mode. Further, for example, when intra prediction isperformed on the current block, a method for rearranging the residualcoefficients may be selected or whether to rearrange the residualcoefficients may be determined based on an intra prediction mode appliedto the current block or the distance between the current block and areference sample used for the intra prediction. In addition, forexample, a method for rearranging the residual coefficients may beselected or whether to rearrange the residual coefficients may bedetermined based on the size of the current block (e.g., the number ofsamples of the current block or the width and height of the currentblock), the shape of the current block (e.g., whether the current blockis a square block or a non-square block), the ratio of the width of thecurrent block to the height thereof, and/or whether quantization isapplied to the current block.

Subsequently, the encoding apparatus may encode information indicatingthe position of the last non-zero residual coefficient of the currentblock (S1520). A syntax element indicating the information indicatingthe position of the last non-zero residual coefficient may belast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix.

Subsequently, the encoding apparatus may encode residual information onthe current block after coded_sub_block_flag, that is, residualinformation encoded after coded_sub_block_flag (S1530). For example, theresidual information may be encoded along with the syntax elementsillustrated in Table 1.

When the value of the transform skip flag is 0, the encoding apparatusmay encode the residual information on the current block as in theexisting method (S1540). For example, the residual information encodedas in the existing method may correspond to the syntax elementsillustrated in Table 1.

Unified transform type information proposed in Table 10 may be signaled.A syntax element of the transform type information may be tu_mts_idx. Inthis case, a method of coding the residual information may be determinedbased on tu_mts_idx. According to the proposed embodiment, it ispossible to reduce the complexity of a process of encoding residualinformation for a block which is not subjected to transform encoding andto improve efficiency in encoding residual information.

FIG. 16 illustrates an example of determining a method of codingresidual information based on unified transform type information.

Referring to FIG. 16, an encoding apparatus may determine whether thevalue of unified transform type information for a current block is 1(S1600). A syntax element of the unified transformation type informationmay be tu_mts_idx.

When the value of the unified transform type information is 1, theencoding apparatus may rearrange residual coefficients of the currentblock (S1610). Here, as a method for rearranging the residualcoefficients, at least one of the foregoing embodiments may be used. Forexample, whether to rearrange the residual coefficients may bedetermined based on whether a prediction mode for the current block isan inter prediction mode or an intra prediction mode. Further, forexample, when intra prediction is performed on the current block, amethod for rearranging the residual coefficients may be selected orwhether to rearrange the residual coefficients may be determined basedon an intra prediction mode applied to the current block or the distancebetween the current block and a reference sample used for the intraprediction. In addition, for example, a method for rearranging theresidual coefficients may be selected or whether to rearrange theresidual coefficients may be determined based on the size of the currentblock (e.g., the number of samples of the current block or the width andheight of the current block), the shape of the current block (e.g.,whether the current block is a square block or a non-square block), theratio of the width of the current block to the height thereof, and/orwhether quantization is applied to the current block.

Subsequently, the encoding apparatus may encode information indicatingthe position of the last non-zero residual coefficient of the currentblock (S1620). A syntax element indicating the information indicatingthe position of the last non-zero residual coefficient may belast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix.

Subsequently, the encoding apparatus may encode residual information onthe current block after coded_sub_block_flag, that is, residualinformation encoded after coded_sub_block_flag (S1630). For example, theresidual information may be encoded along with the syntax elementsillustrated in Table 1.

When the value of the unified transform type information is 0, theencoding apparatus may encode the residual information on the currentblock as in the existing method (S1640). For example, the residualinformation encoded as in the existing method may correspond to thesyntax elements illustrated in Table 1. Further, as illustrated in Table10, syntax elements transform_skip_flag and/or mts_idx may be omitted.According to the proposed embodiment, it is possible to reduce thecomplexity of a process of encoding residual information for a blockwhich is not subjected to transform encoding and to improve efficiencyin encoding residual information.

Meanwhile, a decoding apparatus may derive the residual coefficients ofthe current block based on the residual information as described above,and may determine whether residual rearrangement (residual coefficientrearrangement) is applied to the current block. Whether the residualrearrangement is applied may be determined, for example, based on thevalue of the transform skip flag (i.e., transform_skip_flag) or theunified transform type information (i.e., tu_mts_idx) as shown in FIG.15 or FIG. 16. When the residual rearrangement is applied to the currentblock, the decoding apparatus may rearrange the residual coefficientsbased on a residual rearrangement method determined according to theforegoing criteria, and may derive residual samples for the currentblock based on the rearranged residual coefficients. The residualsamples may be derived from the rearranged residual coefficients, or maybe derived by dequantizing the rearranged residual coefficients asnecessary. Subsequently, as described above, reconstructed samples forthe current block may be generated based on the residual samples andprediction samples for the current block.

As described above, in residual coding for the current block, mainsyntax elements of a 4×4 subblock or 2×2 subblock unit of the currentblock may be sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag,par_level_flag, abs_level_gtX_flag, and abs_remainder. Here, bins forsig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gtX_flag may be context-coded bins coded based on a regularcoding engine, and a bin for abs_remainder may be a bypass bin codedbased on a bypass coding engine.

The context-coded bins are coded using a probability state and rangeupdated by processing a previous bin and thus exhibits high datadependency. That is, the context-coded bins may have difficulty inparallel processing because the next bin can be encoded/decoded afterthe current bin is completely encoded/decoded. Further, it may take along time to derive a probability range and to determine a currentstate. Accordingly, the present disclosure proposes an embodiment ofimproving CABAC processing efficiency by reducing the number ofcontext-coded bins and increasing the number of bypass bins.

According to embodiments of the present disclosure, it is possible toquickly switch from a coding process for syntax elements coded with acontext-coded bin to a coding process for a syntax element abs_remaindercoded based on a bypass coding engine, that is, coded with a bypass bin,and to reduce the number of context-coded bins.

In an embodiment, the present disclosure proposes a method of limitingthe number of residual coefficients coded with sig_coeff_flag,coeff_sign_flag, abs_level_gt1_flag, and par_level_flag in a currentsubblock. That is, the present embodiment proposes a method of limitingthe number of bins allocated for sig sig_coeff_flag, coeff_sign_flag,abs_level_gt1_flag, and par_level_flag to up to N. According to thepresent embodiment, residual coding may be performed on residualcoefficients in a current subblock according to a scan order, and whenthe number of bins coded with sig_coeff_flag, coeff_sign_flag,abs_level_gt1_flag, and par_level_flag, that is, the number of codedcontext-coded bins, reaches N, if abs_level_gt1_flag is not coded insubsequent residual coding, coding abs_level_gtX_flag may not beperformed either and may be switched to coding for abs_remainder. N maydenote the specific number of context-coded bins. That is, when thenumber of context-coded bins for a syntax element(s) proposed within apredetermined region reaches a predetermined value, the remainingtransform coefficient level values of corresponding transformcoefficients and/or the transform coefficient values of subsequenttransform coefficients may be coded with bypass-coded bins inabs_remainder. The same applies to other embodiments below.

For example, when the current subblock is a 4×4 subblock, N may bederived as one of 0 to 64. When the current subblock is a 2×2 subblock,N may be derived as one of 0 to 16. N may be selected by the encodingapparatus. Alternatively, N may be adaptively determined according tothe size of the current block and/or the position of the currentsubblock in the current block. Alternatively, when the current subblockis a 4×4 subblock, N may be set to any one of 0 to 64. When the currentsubblock is a 2×2 subblock, N is may be set to any one of 0 to 16.

In an embodiment, the present disclosure proposes a method of limitingthe number of residual coefficients coded with abs_level_gtX_flag in acurrent subblock. Referring to Table 14, up to four pieces ofabs_level_gtX_flag may be derived for one residual coefficient inresidual coding. That is, when the current subblock is a 4×4 subblock,up to 64 pieces of abs_level_gtX_flags may be coded for the currentsubblock. When the current subblock is a 2×2 subblock, up to 16 piecesof abs_level_gtX_flags may be coded for the current subblock.

Accordingly, the present embodiment proposes a method in which up to Npieces of abs_level_gtX_flag is coded in order to reduce the number ofcontext-coded bins when performing residual coding on residualcoefficients in a current subblock. That is, the present embodimentproposes a method of limiting the number of bins allocated forabs_level_gtX_flag to up to N. N may denote the maximum number of syntaxelements abs_level_gtX_flag. For example, N may be selected by theencoding apparatus. Alternatively, N may be adaptively determinedaccording to the size of the current block and/or the position of thecurrent subblock in the current block. Alternatively, when the currentsubblock is a 4×4 subblock, N may be set to any one of 0 to 64. When thecurrent subblock is a 2×2 subblock, N may be set to any one of 0 to 16.According to the present embodiment, residual coding may be performed onthe residual coefficients in the current subblock according to the scanorder, and when the number of syntax elements abs_level_gtX_flag reachesN, the residual coding may be subsequently switched to coding forabs_remainder. That is, residual coding may be performed on the residualcoefficients in the current subblock according to the scan order, andwhen the number of bins coded with syntax element abs_level_gtX_flag,that is, coded context-coded bins, reaches N, the residual coding may besubsequently switched to coding for abs remainder.

Furthermore, in an embodiment, the present disclosure may propose amethod of combining the foregoing embodiment of limiting the totalnumber of sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, andpar_level_flag with the embodiment of limiting the number ofabs_level_gtX_flag. According to this embodiment, the total number ofsig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, and par_level_flagfor the current subblock may be limited to M, and the number ofabs_level_gtX_flag may be limited to N. That is, the present embodimentproposes a method of limiting the total number of bins allocated forsig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, and par_level_flagto up to M and limiting the number of bins allocated forabs_level_gtX_flag to up to N. Here, when the current subblock is a 4×4subblock, each M and N may be derived as one of 0 to 64. When thecurrent subblock is a 2×2 subblock, each of M and N may be derived asone of 0 to 16.

In addition, in an embodiment, the present disclosure proposes a methodof limiting the number of residual coefficients in one iterationstatement rather than a plurality of iteration statements, for example,the total number of residual coefficients coded with sig_coeff_flag,coeff_sign_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gtX_flag. The foregoing residual coding in Table 14 includesan iteration statement (pass 1) in which sig_coeff_flag,coeff_sign_flag, abs_level_gt1_flag, and par_level_flag are parsed andan iteration statement (pass 2) in which abs_level_gtX_flag is parsed.However, to improve encoding efficiency and to resolve structuralcomplexity when encoding a block to which a transform skip is applied,the present embodiment proposes encoding and decoding (parsing)sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gtX_flag in a single iteration statement. In a case where allthe context-coded bins (sig_coeff_flag, coeff_sign_flag,abs_level_gt1_flag, par_level_flag, and abs_level_gtX_flag) are parsedin one iteration statement, a method of limiting the total number ofcontext-coded bins to N is proposed.

For example, when the current subblock is a 4×4 subblock, N may bederived as one of 0 to 128. When the current subblock is a 2×2 subblock,N may be derived as one of 0 to 32. N may be selected by the encodingapparatus.

Alternatively, N may be adaptively determined according to the size ofthe current block and/or the position of the current subblock in thecurrent block. When the total number of context-coded bins reaches apreset maximum value of N, a syntax element using a context-coded binmay not be coded any more, and coding of abs_remainder coded using thebypass coding engine, that is, coded with a bypass bin, may beperformed. That is, coding may be switched to coding for abs_remaindercoded with a bypass bin.

According to another example, the present disclosure may limit the totalnumber of residual coefficients coded with sig_coeff_flag,abs_level_gt1_flag, and par_level_flag, the number of residualcoefficients coded with abs_level_gtX_flag, and the number of residualcoefficients coded with coeff_sign_flag. The foregoing residual codingin Table 14 includes an iteration statement (pass 1) in whichsig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, and par_level_flagare parsed and an iteration statement (pass 2) in whichabs_level_gtX_flag is parsed. However, to improve encoding efficiencyand to resolve structural complexity when encoding a block to which atransform skip is applied, the present embodiment may separatecoeff_sign_flag from pass 1 and may encode and decode (parse)coeff_sign_flag before pass 1 (in pass 0) or after pass 2 (in pass 3).

According to the present embodiment, the total number of residualcoefficients (the total number of context-coded bins of pass 1) codedwith sig_coeff_flag, abs_level_gt1_flag, and par_level_flag for thecurrent subblock may be limited to N, the number of residualcoefficients (the total number of context-coded bins of pass 2) codedwith abs_level_gtX_flag may be limited to M, and the number of residualcoefficients (the total number of context-coded bins of pass 0 or pass3) coded with coeff_sign_flag may be limited to L.

Here, when the current subblock is a 4×4 subblock, N may be derived asone of 0 to 48, M may be derived as any one of 0 to 64, and L may bederived as one of 0 to 16. Alternatively, when the current subblock is a2×2 subblock, N may be derived as one of 0 to 12, M may be derived asone of 0 to 16, and L may be derived as one of 0 to 4.

N, M, and L may be selected by the encoding apparatus. Alternatively, N,M, and L may be adaptively determined according to the size of thecurrent block and/or the position of the current subblock in the currentblock.

According to another embodiment, the present disclosure may limit thetotal number of residual coefficients coded with sig_coeff_flag,abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag and the number ofresidual coefficients coded with coeff_sign_flag. The foregoing residualcoding in Table 14 includes an iteration statement (pass 1) in whichsig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, and par_level_flagare parsed and an iteration statement (pass 2) in whichabs_level_gtX_flag is parsed. However, to improve encoding efficiencyand to resolve structural complexity when encoding a block to which atransform skip is applied, the present embodiment may parsesig_coeff_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gtX_flag in a single iteration statement (pass 1′) excludingcoeff_sign_flag and may encode and decode (parse) coeff_sign_flag,excluded from pass 1, before pass 1 (in pass 0′) or after pass 2 (inpass 2′).

According to the present embodiment, the total number of residualcoefficients (the total number of context-coded bins of pass 1′) codedwith sig_coeff_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gtX_flag for the current subblock may be limited to N, and thenumber of residual coefficients (the total number of context-coded binsof pass 0′ or pass 2′) coded with coeff_sign_flag may be limited to M.

Here, when the current subblock is a 4×4 subblock, N may be derived asone of 0 to 112, and M may be derived as any one of 0 to 16.Alternatively, when the current subblock is a 2×2 subblock, N may bederived as one of 0 to 28, and M may be derived as one of 0 to 4.

N and M may be selected by the encoding apparatus. Alternatively, N andM may be adaptively determined according to the size of the currentblock and/or the position of the current subblock in the current block.

FIG. 17 schematically illustrates an image encoding method by anencoding apparatus according to the present disclosure. The methodillustrated in FIG. 17 may be performed by the encoding apparatusillustrated in FIG. 2. Specifically, for example, S1700 of FIG. 17 maybe performed by the subtractor of the encoding apparatus, S1710 may beperformed by the transformer and the quantizer of the encodingapparatus, and S1720 to S1750 may be performed by the entropy encoder ofthe encoding apparatus. Further, although not shown, a process ofderiving a prediction sample may be performed by the predictor of theencoding apparatus, a process of deriving reconstructed samples for acurrent block based on residual samples and prediction samples for thecurrent block may be performed by the adder of the encoding apparatus,and a process of encoding prediction information on the current blockmay be performed by the entropy encoder of the encoding apparatus.

The encoding apparatus derives residual samples for a current block(S1700). The encoding apparatus may determine whether to perform interprediction or intra prediction on the current block and may determine aspecific inter prediction mode or a specific intra prediction mode basedon RD cost. The encoding apparatus may derive prediction samples for thecurrent block according to the determined mode and may derive theresidual samples by subtracting the prediction samples from originalsamples for the current block.

The encoding apparatus derives transform coefficients in a currentsubblock of the current block based on the residual samples (S1710). Theencoding apparatus may derive the transform coefficients based on theresidual samples in the current subblock of the current block.

For example, the encoding apparatus may determine whether a transform isapplied to the residual samples. When no transform is applied to theresidual samples, the encoding apparatus may derive the derived residualsamples as the transform coefficients. When the transform is applied tothe residual samples, the encoding apparatus may derive the transformcoefficients by transforming the derived residual samples. The transformcoefficients may be included in the current subblock of the currentblock. The current subblock may be referred to as a current coefficientgroup (CG). The current subblock of the current block may have a 4×4size or a 2×2 size. That is, the current subblock of the current blockmay include up to 16 non-zero transform coefficients or up to fournon-zero transform coefficients.

The encoding apparatus may generate and encode a transform skip flagindicating whether the transform is applied to the transformcoefficients of the current block. A bitstream may include the transformskip flag for the current block. The transform skip flag may indicatewhether the transform is applied to the transform coefficients of thecurrent block. That is, the transform skip flag may indicate whether thetransform has been applied to the transform coefficients. A syntaxelement indicating the transform skip flag may be transform_skip_flagillustrated above.

When the value of the transform skip flag for the current block is 1,the encoding apparatus may rearrange the transform coefficients. In thiscase, the encoding apparatus may generate and encode residualinformation on the rearranged transform coefficients. For example, theencoding apparatus may rearrange the transform coefficients throughvarious rearrangement methods. That is, the encoding apparatus maytransfer the transform coefficients from a derived position to adifferent position through various rearrangement methods.

In one example, the encoding apparatus may rearrange the transformcoefficients through a rearrangement method of 180-degree rotation.Specifically, for example, the encoding apparatus may rearrange thetransform coefficients of the current block to symmetrical positionswith respect to the center of the current block.

Alternatively, in one example, the encoding apparatus may rearrange thetransform coefficients through a rearrangement method of antidiagonalmirroring. Specifically, for example, the encoding apparatus mayrearrange the transform coefficients to symmetrical positions withrespect to a right upward diagonal of the current block. Here, the rightupward diagonal may refer to a right upward diagonal passing through thecenter of the current block.

Alternatively, in one example, the encoding apparatus may rearrange thetransform coefficients through a rearrangement method of main diagonalmirroring. Specifically, for example, the encoding apparatus mayrearrange the transform coefficients to symmetrical positions withrespect to the left upward diagonal of the current block. Here, the leftupward diagonal may refer to a left upward diagonal passing through thecenter of the current block.

Alternatively, in one example, the encoding apparatus may rearrange thetransform coefficients through a rearrangement method of verticalflipping. Specifically, for example, the encoding apparatus mayrearrange the transform coefficients of the current block to symmetricalpositions with respect to a vertical axis of the current block. Here,the vertical axis may be a vertical line passing through the center ofthe current block.

Alternatively, in one example, the encoding apparatus may rearrange thetransform coefficients through a rearrangement method of horizontalflipping. The encoding apparatus may rearrange the transformcoefficients of the current block to symmetrical positions with respectto a horizontal axis of the current block. Here, the horizontal axis maybe a horizontal line passing through the center of the current block.

Alternatively, in one example, the encoding apparatus may rearrange thetransform coefficients through a method of deriving separate layersbased on the distance to a reference sample of the current block andrearranging the layers according to an inverse raster order.

For example, the encoding apparatus may set layers for the current blockbased on distances from reference samples of the current block. Here,the reference samples may include top reference samples and leftreference samples of the current block. For example, when the size ofthe current block is N×N and an x component of the position of atop-left sample position of the current block is 0 and the y componentthereof is 0, the left reference samples may be p[−1][0] to p[−1][2N−1],and the top reference samples may be p[0][−1] to p[2N−1][−1]. When thesize of the current block is N×N, the layers may include a first layerto an Nth layer. The Nth layer may be the last layer, and N may be equalto the width or the height of the current block. For example, the firstlayer may include positions from which the distance to the nearestreference sample is 1, a second layer may include positions having fromwhich the distance to the nearest reference sample is 2, and the Nthlayer may include positions from which the distance to the nearestreference sample is N.

Subsequently, the encoding apparatus may scan the transform coefficientsin the inverse raster order. That is, the encoding apparatus may scanthe transform coefficients of the current block from right to left andfrom bottom to top. Next, the encoding apparatus may rearrange thetransform coefficients in the layers in the scan order. Here, thetransform coefficients may be rearranged in an order from the firstlayer to the Nth layer. The transform coefficients may be rearrangedbased on a transverse-first scan or a longitudinal-first scan in therearranged layers.

For example, the transform coefficients may be preferentially rearrangedfrom right to left at lateral positions of the top-left position of therearranged layers, and when there are longitudinal positions of thetop-left position of the rearranged layers, the transform coefficientsmay be rearranged from top to bottom at the longitudinal positions ofthe top-left position of the rearranged layers after being arranged atthe lateral positions. Alternatively, for example, the transformcoefficients may be preferentially rearranged from top to bottom atlongitudinal positions of the top-left position of the rearrangedlayers, and when there are lateral positions of the top-left position ofthe rearranged layers, the transform coefficients may be rearranged fromleft to right at the lateral positions of the top-left position of therearranged layers after being arranged at the longitudinal positions.

Alternatively, in one example, the encoding apparatus may rearrange thetransform coefficients through a method of deriving separate layersbased on a distance to a reference sample of the current block andrearranging the layers according to a diagonal scan order.

For example, the encoding apparatus may set layers for the current blockbased on distances from reference samples of the current block. Here,the reference samples may include top reference samples and leftreference samples of the current block. For example, when the size ofthe current block is N×N and an x component of the position of atop-left sample position of the current block is 0 and the y componentthereof is 0, the left reference samples may be p[−1][0] to p[−1][2N−1],and the top reference samples may be p[0][−1] to p[2N−1][−1]. When thesize of the current block is N×N, the layers may include a first layerto an Nth layer. The Nth layer may be the last layer, and N may be equalto the width or the height of the current block. For example, the firstlayer may include positions from which the distance to the nearestreference sample is 1, a second layer may include positions having fromwhich the distance to the nearest reference sample is 2, and the Nthlayer may include positions from which the distance to the nearestreference sample is N.

Subsequently, the encoding apparatus may scan the transform coefficientsin the diagonal scan order. That is, the encoding apparatus may scan thetransform coefficients of the current block from top right to bottomleft and from bottom right to top left. Next, the encoding apparatus mayrearrange the transform coefficients in the layers in the scan order.Here, the transform coefficients may be rearranged in an order from thefirst layer to the Nth layer. The transform coefficients may berearranged based on a transverse-first scan or a longitudinal-first scanin the rearranged layers.

For example, the transform coefficients may be preferentially rearrangedfrom right to left at lateral positions of the top-left position of therearranged layers, and when there are longitudinal positions of thetop-left position of the rearranged layers, the transform coefficientsmay be rearranged from top to bottom at the longitudinal positions ofthe top-left position of the rearranged layers after being arranged atthe lateral positions. Alternatively, for example, the transformcoefficients may be preferentially rearranged from top to bottom atlongitudinal positions of the top-left position of the rearrangedlayers, and when there are lateral positions of the top-left position ofthe rearranged layers, the transform coefficients may be rearranged fromleft to right at the lateral positions of the top-left position of therearranged layers after being arranged at the longitudinal positions.

Alternatively, for example, the encoding apparatus may set layers forthe current block based on distances from top reference samples of thecurrent block. For example, when the size of the current block is N×Nand an x component of the position of a top-left sample position of thecurrent block is 0 and the y component thereof is 0, the top referencesamples may be p[0][−1] to p[2N−1][−1]. When the size of the currentblock is N×N, the layers may include a first layer to an Nth layer. TheNth layer may be the last layer, and N may be equal to the width or theheight of the current block. For example, the first layer may includepositions from which the distance to the nearest top reference sample is1, a second layer may include positions having from which the distanceto the nearest top reference sample is 2, and the Nth layer may includepositions from which the distance to the nearest top reference sample isN. That is, the first layer may be a first row of the current block, thesecond layer may be a second row of the current block, and the Nth layermay be an Nth row of the current block.

Subsequently, the encoding apparatus may scan the transform coefficientsin the diagonal scan order. That is, the encoding apparatus may scan thetransform coefficients of the current block from top right to bottomleft and from bottom right to top left. Next, the encoding apparatus mayrearrange the transform coefficients in the layers in the scan order.Here, the transform coefficients may be rearranged in an order from thefirst layer to the Nth layer. Rearrangement of the transformcoefficients may be performed in the order from the first layer to theNth layer, and the transform coefficients may be rearranged based fromright to left at the positions of the rearranged layers.

Alternatively, for example, the encoding apparatus may set layers forthe current block based on distances from left reference samples of thecurrent block. For example, when the size of the current block is N×Nand an x component of the position of a top-left sample position of thecurrent block is 0 and the y component thereof is 0, the left referencesamples may be p[−1][0] to p[−1][2N−1]. When the size of the currentblock is N×N, the layers may include a first layer to an Nth layer. TheNth layer may be the last layer, and N may be equal to the width or theheight of the current block. For example, the first layer may includepositions from which the distance to the nearest left reference sampleis 1, a second layer may include positions having from which thedistance to the nearest left reference sample is 2, and the Nth layermay include positions from which the distance to the nearest leftreference sample is N. That is, the first layer may be a first column ofthe current block, the second layer may be a second column of thecurrent block, and the Nth layer may be an Nth column of the currentblock.

Subsequently, the encoding apparatus may scan the transform coefficientsin the diagonal scan order. That is, the encoding apparatus may scan thetransform coefficients of the current block from top right to bottomleft and from bottom right to top left. Next, the encoding apparatus mayrearrange the transform coefficients in the layers in the scan order.Here, the transform coefficients may be rearranged in an order from thefirst layer to the Nth layer. Rearrangement of the transformcoefficients may be performed in the order from the first layer to theNth layer, and the transform coefficients may be rearranged based fromtop to bottom at the positions of the rearranged layers.

The encoding apparatus may determine whether to rearrange the transformcoefficients based on various conditions. Alternatively, the encodingapparatus may derive a rearrangement method applied to the transformcoefficients based on various conditions.

For example, the encoding apparatus may determine whether to rearrangethe transform coefficients based on the transform skip flag for thecurrent block. The transform skip flag may indicate whether thetransform is applied to the transform coefficients. For example, whenthe value of the transform skip flag is 1, it may be determined torearrange the transform coefficients. That is, when the value of thetransform skip flag is 1, the encoding apparatus may rearrange thetransform coefficients. When the value of the transform skip flag is 0,it may be determined not to rearrange the transform coefficients. Thatis, when the value of the transform skip flag is 0, the encodingapparatus may generate and encode residual information on the currentblock based on the transform coefficients rather than rearranging thetransform coefficients.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on the number of samples of thecurrent block. For example, when the number of samples of the currentblock is less than a specific value, it may be determined to rearrangethe transform coefficients. That is, when the number of samples of thecurrent block is smaller than the specific value, the encoding apparatusmay rearrange the transform coefficients. When the number of samples ofthe current block is the specific value or greater, it may be determinednot to rearrange the transform coefficients. That is, when the number ofsamples of the current block is the specific value or greater, theencoding apparatus may generate and encode residual information on thecurrent block based on the transform coefficients rather thanrearranging the transform coefficients. The specific value may be 64.

Alternatively, for example, when the number of samples of the currentblock is less than 64, the encoding apparatus may rearrange thetransform coefficients through the rearrangement method of 180-degreerotation. When the number of samples of the current block is 64 orgreater, the encoding apparatus may not rearrange the transformcoefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on the number of samplesof the current block.

For example, when the number of samples of the current block is lessthan 64, the encoding apparatus may rearrange the transform coefficientsthrough the rearrangement method of 180-degree rotation, and when thenumber of samples of the current block is 64 or greater, the encodingapparatus may rearrange the transform coefficients through therearrangement method of mirroring. Alternatively, in another example,when the number of samples of the current block is less than 64, theencoding apparatus may rearrange the transform coefficients through oneof the rearrangement methods described above, and when the number ofsamples of the current block is 64 or greater, the encoding apparatusmay not rearrange the transform coefficients.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on the shape of the current block.For example, when the current block is a square block, it may bedetermined to rearrange the transform coefficients. That is, when thecurrent block is a square block, the encoding apparatus may rearrangethe transform coefficients. When the current block is a non-squareblock, it may be determined not to rearrange the transform coefficients.That is, when the current block is a non-square block, the encodingapparatus may generate and encode residual information on the currentblock based on the transform coefficients rather than rearranging thetransform coefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on the shape of thecurrent block. For example, when the current block is a square block,the encoding apparatus may rearrange the transform coefficients throughthe rearrangement method of mirroring, and when the current block is anon-square block, the encoding apparatus may rearrange the transformcoefficients through the rearrangement method of 180-degree rotation.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on the ratio of the width of thecurrent block to the height thereof. For example, when the ratio of thewidth of the current block to the height is 2 or greater or is ½ or less(i.e., when a value obtained by dividing the width of the current blockby the height is 2 or greater or is ½ or less), the encoding apparatusmay rearrange the transform coefficients through the rearrangementmethod of mirroring, and when the ratio of the width of the currentblock to the height is less than 2 and is greater than ½ (i.e., thevalue obtained by dividing the width of the current block by the heightis less than 2 and is greater than ½), the encoding apparatus maygenerate and encode residual information on the current block based onthe transform coefficients rather than rearranging the transformcoefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on the ratio of the widthof the current block to the height thereof. For example, when the ratioof the width of the current block to the height is 2 or greater or is ½or less (i.e., when a value obtained by dividing the width of thecurrent block by the height is 2 or greater or is ½ or less), theencoding apparatus may rearrange the transform coefficients through therearrangement method of mirroring, and when the ratio of the width ofthe current block to the height is less than 2 and is greater than ½(i.e., the value obtained by dividing the width of the current block bythe height is less than 2 and is greater than ½), the encoding apparatusmay rearrange the transform coefficients through the rearrangementmethod of 180-degree rotation.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on an intra prediction mode for thecurrent block. For example, when the prediction direction of the intraprediction mode for the current block is a horizontal direction or theintra prediction mode for the current block is an intra prediction modein which prediction is performed mainly using a left reference sample,the encoding apparatus may rearrange the transform coefficients throughthe rearrangement method vertical flipping, and in other cases, theencoding apparatus may generate and encode residual information on thecurrent block based on the transform coefficients rather thanrearranging the transform coefficients. Alternatively, for example, whenthe prediction direction of the intra prediction mode for the currentblock is a vertical direction or the intra prediction mode for thecurrent block is an intra prediction mode in which prediction isperformed mainly using a top reference sample, the encoding apparatusmay rearrange the transform coefficients through the rearrangementmethod vertical flipping, and in other cases, the encoding apparatus maygenerate and encode residual information on the current block based onthe transform coefficients rather than rearranging the transformcoefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on an intra predictionmode for the current block. For example, when the prediction directionof the intra prediction mode for the current block is a horizontaldirection or the intra prediction mode for the current block is an intraprediction mode in which prediction is performed mainly using a leftreference sample, the encoding apparatus may rearrange the transformcoefficients through the rearrangement method vertical flipping, andwhen the prediction direction of the intra prediction mode for thecurrent block is a vertical direction or the intra prediction mode forthe current block is an intra prediction mode in which prediction isperformed mainly using a top reference sample, the encoding apparatusmay rearrange the transform coefficients through the rearrangementmethod vertical flipping.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on a flag indicating whether torearrange the transform coefficients, which is signaled through ahigh-level syntax. For example, the encoding apparatus may signal theflag indicating whether to rearrange the transform coefficients througha sequence parameter set (SPS) or a picture parameter set (PPS) and maydetermine whether to rearrange the transform coefficients based on theflag.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on information indicatingthe rearrangement method for the transform coefficients, which issignaled through a high-level syntax. For example, the encodingapparatus may signal the information indicating the rearrangement methodfor the transform coefficients through a sequence parameter set (SPS) ora picture parameter set (PPS) and may determine whether to rearrange thetransform coefficients based on the information.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on a prediction mode for thecurrent block. For example, when the prediction mode for the currentblock is intra prediction, it may be determined to rearrange thetransform coefficients. That is, when the prediction mode for thecurrent block is intra prediction, the encoding apparatus may rearrangethe transform coefficients. When the prediction mode for the currentblock is inter prediction, it may be determined not to rearrange thetransform coefficients. That is, when the prediction mode for thecurrent block is inter prediction, the encoding apparatus may generateand encode residual information on the current block based on thetransform coefficients rather than rearranging the transformcoefficients.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on whether the transformcoefficients are quantized. For example, when quantization has beenapplied to the transform coefficients, it may be determined to rearrangethe transform coefficients. That is, when quantization has been appliedto the transform coefficients, the encoding apparatus may rearrange thetransform coefficients. When no quantization has been applied to thetransform coefficients, it may be determined not to rearrange thetransform coefficients. That is, when no quantization has been appliedto the transform coefficients, the encoding apparatus may not rearrangethe transform coefficients.

The encoding apparatus derives a specific number for the number ofcontext-coded bins for context syntax elements for the current subblock(S1720). Here, the specific number may be the foregoing maximum value,and the maximum value may be the maximum value of the total number ofcontext-coded bins for the context syntax elements for the transformcoefficients related to the current subblock of the current block.

For example, the specific number may be derived by a unit of a transformblock.

For example, the specific number may be set to an arbitrary value. Whenthe size of the current subblock is 4×4, the specific number may bederived as one value of 0 to 64, and when the size of the currentsubblock is 2×2, the specific number may be derived as one value of 0 to16. For example, the specific number may be set to 4.

Alternatively, for example, the specific number may be derived based onthe size of the current block (or the current subblock in the currentblock). When the size of the current block (or the current subblock inthe current block) is 4×4, the derived specific number may be derived asone value of 0 to 64, and when the current block (or the currentsubblock in the current block) is 2×2, the derived specific number maybe derived as one value of 0 to 16.

Alternatively, for example, the specific number may be derived based onthe size of the current block and the position of the current subblock.

Alternatively, for example, the specific number may be derived based onposition information indicating the position of the last non-zerotransform coefficient of the current block. For example, the position ofthe last non-zero transform coefficient may be derived based on theposition information, and the length from the position of the startingtransform coefficient in the scan order of the current block to theposition of the last non-zero transform coefficient may be derived. Thespecific number may be derived based on the length. For example, thespecific number may be derived as a value obtained by multiplying thelength by 1.75. The length may correspond to the number of samples ofthe current block. That is, the length may be the number of samples ofthe current block. For example, when a transform coefficient having avalue of 0 is not included in a transform coefficient array of thecurrent block, the length may be the number of samples of the currentblock. That is, the specific number may be derived based on the numberof samples of the current block. For example, the specific number may bederived as a value obtained by multiplying the number of samples of thecurrent block by 1.75.

The encoding apparatus may encode the context syntax elements based onthe specific number and, more specifically, may encode the differentcontext syntax elements based on the specific number according towhether a transform skip is applied to the current block. For example,when the transform skip is applied to the current block, the encodingapparatus may encode preset context syntax elements, for example,sig_coeff_flag, coeff_sign_flag, par_level_flag, abs_level_gt1_flag, andabs_level_gtx_flag, based on a context model until the specific numberfor the transform coefficients arrives. (S1730). Subsequently, theencoding apparatus may encode remaining transform coefficients based ona bypass model (S1740).

For example, when the transform skip is applied to the current block,the encoding apparatus may encode the context syntax elements of atransform coefficient for the current subblock of the current blockbased on context. The context syntax elements may include a significantcoefficient flag indicating whether the transform coefficient is anon-zero transform coefficient, a sign flag indicating the sign of thetransform coefficient, a first transform coefficient level flagindicating whether the level of the transform coefficient is greaterthan a first threshold, a parity level flag indicating the parity of thetransform coefficient level of the transform coefficient, and a secondtransform coefficient level flag indicating whether the transformcoefficient level of the transform coefficient is greater than a secondthreshold. The significant coefficient flag may be sig_coeff_flag, thesign flag may be coeff_sign_flag, the first transform coefficient levelflag may be abs_level_gt1_flag or abs_level_gtx_flag, the parity levelflag may be par_level_flag, and the second transform coefficient levelflag may be abs_level_gt3_flag or abs_level_gtx_flag. For example, whenthe second transform coefficient level flag is expressed asabs_level_gtx_flag, the flag may be encoded according to a certainiteration statement, and thus the second transform coefficient levelflag is not a single value but may be a third transform coefficientlevel, a fourth transform coefficient level, a fifth transformcoefficient level, or the like, which is different from the secondtransform coefficient level.

Alternatively, when the transform skip is not applied to the currentblock, the encoding apparatus may encode the context syntax elements ofa transform coefficient for the current subblock of the current blockbased on context.

For example, the context syntax elements may include a significantcoefficient flag indicating whether the transform coefficient is anon-zero transform coefficients, a first transform coefficient levelflag indicating whether the level of the transform coefficient isgreater than a first threshold, a parity level flag indicating theparity of the transform coefficient level of the transform coefficient,and a second transform coefficient level flag indicating whether thetransform coefficient level of the transform coefficient is greater thana second threshold. The first transform coefficient level flag may beabs_level_gt1_flag or abs_level_gtx_flag, the parity level flag may bepar_level_flag, and the second transform coefficient level flag may beabs_level_gt3_flag or abs_level_gtx_flag. For example, when the secondtransform coefficient level flag is expressed as abs_level_gtx_flag, theflag may be encoded according to a certain iteration statement, and thusthe second transform coefficient level flag is not a single value butmay be a third transform coefficient level, a fourth transformcoefficient level, a fifth transform coefficient level, or the like,which is different from the second transform coefficient level.

Specifically, when the total number of context-coded bins of contextsyntax elements for transform coefficients preceding a transformcoefficient in the scan order among the transform coefficients for thecurrent subblock reaches the specific number (i.e., is the specificnumber or greater), signaling of context syntax elements for thetransform coefficient may be omitted (i.e., the context syntax elementsfor the transform coefficient may not be signaled), and a bypass syntaxelement that is bypass-coded for the transform coefficient may beencoded. That is, the value of the transform coefficient may be codedbased on the bypass syntax element that is bypass-coded.

For example, when the total number of context-coded bins for contextsyntax elements of transform coefficient 0 to transform coefficient n ofthe current subblock reaches the specific number, signaling of contextsyntax elements for transform coefficient n+1 of the current subblockmay be omitted, and a bypass syntax element for the n+1th transformcoefficient included in the residual information may be encoded. Thatis, the value of transform coefficient n+1 may be encoded based on thevalue of the bypass syntax element.

That is, for example, when the transform skip is applied to the currentblock, if the total number of context-coded bins for significantcoefficient flags, sign flags, first transform coefficient level flags,parity level flags, and second transform coefficient level flags fortransform coefficient 0 to transform coefficient n determined by thescan order among the transform coefficients for the current subblockreaches the specific number (i.e., is the specific number or greater),signaling of a significant coefficient flag, a sign flag, a firsttransform coefficient level flag, a parity level flag, and a secondtransform coefficient level flag for transform coefficient n+1determined by the scan order may be omitted, and a bypass syntax elementthat is bypass-coded for quantized transform coefficient n+1 may beencoded. Here, the bypass syntax element may include abs_remainder ofthe absolute value of the remainder of a transform coefficient levelcoded at a predetermined scanning position.

In summary, in coding the transform coefficients, the abs_remainder ofthe absolute value of the remainder of the transform coefficient levelmay refer to (1) a remaining value after coding, such as significantcoefficient flags, sign flags, first transform coefficient level flags,parity level flags, a second transform coefficient level flag, a thirdtransform coefficient level, and a fifth transform coefficient level,according to a level value when the total number of context-coded binsdoes not reach the specific number, or (2) the absolute value of anactual transform coefficient when the total number of context-coded binsreaches the specific number.

Alternatively, for example, when the transform skip is not applied tothe current block, if the total number of context-coded bins forsignificant coefficient flags, first transform coefficient level flags,parity level flags, and second transform coefficient level flags fortransform coefficient 0 to transform coefficient n determined by thescan order among the transform coefficients for the current subblockreaches the specific number (i.e., is the specific number or greater),signaling of a significant coefficient flag, a first transformcoefficient level flag, a parity level flag, and a second transformcoefficient level flag for transform coefficient n+1 determined by thescan order may be omitted, and a bypass syntax element that isbypass-coded for quantized transform coefficient n+1 may be encoded.Here, the bypass syntax element may include abs_remainder of theabsolute value of the remainder of a transform coefficient level codedat a predetermined scanning position and dec_abs_level indicating anintermediate value coded with a Golomb-Rice code at a scanning position.

The encoding apparatus generates a bitstream including the residualinformation on the current block including the encoded context syntaxelements and bypass syntax elements (S1750). For example, the encodingapparatus may output image information including the residualinformation as a bitstream.

For example, the residual information may include syntax elements, suchas transform_skip_flag, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag,abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainder,coeff_sign_flag, dec_abs_level, and/or mts_idx.

Specifically, for example, the residual information may include thetransform skip flag for the current block. The transform skip flag mayindicate whether the transform is applied to the transform coefficientsof the current block. That is, the transform skip flag may indicatewhether the transform has been applied to the transform coefficients.The syntax element indicating the transform skip flag may betransform_skip_flag described above.

Further, for example, the residual information may include the positioninformation indicating the position of the last non-zero transformcoefficient in the transform coefficient array of the current block.That is, the residual information may include the position informationindicating the position of the last non-zero transform coefficient inthe scan order of the current block. The position information mayinclude information indicating a prefix of a column position of the lastnon-zero coefficient, information indicating a prefix of a row positionof the last non-zero coefficient, information indicating a suffix of thecolumn position of the last non-zero coefficient, and informationindicating a suffix of the row position of the last non-zerocoefficient. Syntax elements for the position information may belast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix. The non-zerotransform coefficient may also be referred to as a significantcoefficient.

In addition, for example, the residual information may include contextsyntax elements coded based on the context of a transform coefficient inthe current subblock of the current block. The context syntax elementsmay include a significant coefficient flag indicating whether thetransform coefficient is a non-zero transform coefficient, a firsttransform coefficient level flag indicating whether the level of thetransform coefficient is greater than a first threshold, a parity levelflag indicating the parity of the transform coefficient level of thetransform coefficient, and a second transform coefficient level flagindicating whether the transform coefficient level of the transformcoefficient is greater than a second threshold. The significantcoefficient flag may be sig_coeff_flag, the first transform coefficientlevel flag may be abs_level_gt1_flag, the parity level flag may bepar_level_flag, and the second transform coefficient level flag may beabs_level_gt3_flag or abs_level_gtx_flag.

Alternatively, for example, the context syntax elements may include asignificant coefficient flag indicating whether the transformcoefficient is a non-zero transform coefficient, a sign flag indicatingthe sign of the transform coefficient, a first transform coefficientlevel flag indicating whether the level of the transform coefficient isgreater than a first threshold, and a parity level flag indicating theparity of the transform coefficient level of the transform coefficient.The significant coefficient flag may be sig_coeff_flag, the sign flagmay be coeff_sign_flag, the first transform coefficient level flag maybe abs_level_gt1_flag, and the parity level flag may be par_level_flag.

Furthermore, for example, the residual information may include a bypasssyntax element coded based on a bypass for a transform coefficient inthe current subblock of the current block. The bypass syntax element mayinclude coefficient value-related information on the value of thetransform coefficient. The coefficient value-related information may beabs remainder and/or dec_abs_level.

The bitstream may include prediction information on the current block.The prediction information may include information on an interprediction mode or an intra prediction mode performed on the currentblock. The encoding apparatus may generate and encode the predictioninformation on the current block.

The bitstream may be transmitted to a decoding apparatus through anetwork or a (digital) storage medium. The network may include abroadcast network and/or a communication network, and the digitalstorage medium may include various storage media, such as a USB, an SD,a CD, a DVD, a Blu-ray, an HDD, and an SSD.

FIG. 18 schematically illustrates an encoding apparatus that performs animage encoding method according to the present disclosure. The methodillustrated in FIG. 17 may be performed by the encoding apparatusillustrated in FIG. 18. Specifically, for example, a subtractor of theencoding apparatus of FIG. 18 may perform S1700 of FIG. 17, a residualrearranger of the encoding apparatus of FIG. 18 may perform S1710 ofFIG. 17, and an entropy encoder of the encoding apparatus of FIG. 18 mayperform S1720 to S1750. Further, although not shown, a process ofderiving a prediction sample may be performed by the predictor of theencoding apparatus, a process of deriving reconstructed samples for acurrent block based on residual samples and prediction samples for thecurrent block may be performed by the adder of the encoding apparatus,and a process of encoding prediction information on the current blockmay be performed by the entropy encoder of the encoding apparatus.

FIG. 19 schematically illustrates an image decoding method by a decodingapparatus according to the present disclosure. The method illustrated inFIG. 19 may be performed by the decoding apparatus illustrated in FIG.3. Specifically, for example, S1900 to S1930 of FIG. 19 may be performedby the entropy decoder of the decoding apparatus, S1940 and S1950 may beperformed by the dequantizer and the inverse transformer of the decodingapparatus, and S1960 may be performed by the adder of the decodingapparatus. Further, although not shown, a process of deriving aprediction sample may be performed by the predictor of the decodingapparatus, a process of deriving reconstructed samples for a currentblock based on residual samples and prediction samples for the currentblock may be performed by the adder of the encoding apparatus, and aprocess of encoding prediction information on the current block may beperformed by the entropy encoder of the encoding apparatus.

The decoding apparatus receives a bitstream including residualinformation on the current block (S1900). The decoding apparatus mayreceive image information including the residual information the currentblock through the bitstream. Here, the current block may be a codingblock (CB) or a transform block (TB). The residual information mayinclude syntax elements for a current subblock in the current block.Here, the syntax elements may include context syntax elements and bypasssyntax elements. That is, the residual information may include thecontext syntax elements and the bypass syntax elements for the currentsubblock. The context syntax elements may denote syntax elements codedbased on context, and the bypass syntax elements may denote bypass-codedsyntax elements (i.e., syntax elements coded based on uniformprobability distribution).

For example, the residual information may include syntax elements, suchas transform_skip_flag, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag,abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainder,coeff_sign_flag, dec_abs_level, and/or mts_idx.

Specifically, for example, the residual information may include atransform skip flag for the current block. The transform skip flag mayindicate whether the transform is applied to the transform coefficientsof the current block. That is, the transform skip flag may indicatewhether the transform has been applied to the transform coefficients. Asyntax element indicating the transform skip flag may betransform_skip_flag illustrated above.

Further, for example, the residual information may include positioninformation indicating the position of the last non-zero transformcoefficient in a transform coefficient array of the current block. Thatis, the residual information may include the position informationindicating the position of the last non-zero transform coefficient inthe scan order of the current block. The position information mayinclude information indicating a prefix of a column position of the lastnon-zero coefficient, information indicating a prefix of a row positionof the last non-zero coefficient, information indicating a suffix of thecolumn position of the last non-zero coefficient, and informationindicating a suffix of the row position of the last non-zerocoefficient. Syntax elements for the position information may belast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix. The non-zerotransform coefficient may also be referred to as a significantcoefficient.

In addition, for example, the residual information may include contextsyntax elements coded based on the context of a transform coefficient inthe current subblock of the current block. The context syntax elementsmay include a significant coefficient flag indicating whether thetransform coefficient is a non-zero transform coefficient, a firsttransform coefficient level flag indicating whether the level of thetransform coefficient is greater than a first threshold, a parity levelflag indicating the parity of the transform coefficient level of thetransform coefficient, and a second transform coefficient level flagindicating whether the transform coefficient level of the transformcoefficient is greater than a second threshold. The significantcoefficient flag may be sig_coeff_flag, the first transform coefficientlevel flag may be abs_level_gt1_flag, the parity level flag may bepar_level_flag, and the second transform coefficient level flag may beabs_level_gt3_flag or abs_level_gtx_flag.

Alternatively, for example, the context syntax elements may include asignificant coefficient flag indicating whether the transformcoefficient is a non-zero transform coefficient, a sign flag indicatingthe sign of the transform coefficient, a first transform coefficientlevel flag indicating whether the level of the transform coefficient isgreater than a first threshold, and a parity level flag indicating theparity of the transform coefficient level of the transform coefficient.The significant coefficient flag may be sig_coeff_flag, the sign flagmay be coeff_sign_flag, the first transform coefficient level flag maybe abs_level_gt1_flag, and the parity level flag may be par_level_flag.

Furthermore, for example, the residual information may include a bypasssyntax element coded based on a bypass for a transform coefficient inthe current subblock of the current block. The bypass syntax element mayinclude coefficient value-related information on the value of thetransform coefficient. The coefficient value-related information may beabs remainder and/or dec_abs_level.

The bitstream may include prediction information on the current block.The prediction information may include information on an interprediction mode or an intra prediction mode performed on the currentblock. The decoding apparatus may perform inter prediction or intraprediction on the current block based on the prediction informationreceived through the bitstream and may derive prediction samples of thecurrent block.

The decoding apparatus derives a specific number for the number ofcontext-coded bins for the context syntax elements for the currentsubblock of the current block (S1910). Here, the specific number may bethe foregoing maximum value, and the maximum value may be the maximumvalue of the total number of context-coded bins for the context syntaxelements for the transform coefficients related to the current subblockof the current block.

For example, the specific number may be derived by a unit of a transformblock.

For example, the specific number may be set to an arbitrary value. Whenthe size of the current subblock is 4×4, the specific number may bederived as one value of 0 to 64, and when the size of the currentsubblock is 2×2, the specific number may be derived as one value of 0 to16. For example, the specific number may be set to 4.

Alternatively, for example, the specific number may be derived based onthe size of the current block (or the current subblock in the currentblock). When the size of the current block (or the current subblock inthe current block) is 4×4, the derived specific number may be derived asone value of 0 to 64, and when the current block (or the currentsubblock in the current block) is 2×2, the derived specific number maybe derived as one value of 0 to 16.

Alternatively, for example, the specific number may be derived based onthe size of the current block and the position of the current subblock.

Alternatively, for example, the specific number may be derived based onposition information indicating the position of the last non-zerotransform coefficient of the current block. For example, the position ofthe last non-zero transform coefficient may be derived based on theposition information, and the length from the position of the startingtransform coefficient in the scan order of the current block to theposition of the last non-zero transform coefficient may be derived. Thespecific number may be derived based on the length. For example, thespecific number may be derived as a value obtained by multiplying thelength by 1.75. The length may correspond to the number of samples ofthe current block. That is, the length may be the number of samples ofthe current block. For example, when a transform coefficient having avalue of 0 is not included in a transform coefficient array of thecurrent block, the length may be the number of samples of the currentblock. That is, the specific number may be derived based on the numberof samples of the current block. For example, the specific number may bederived as a value obtained by multiplying the number of samples of thecurrent block by 1.75.

The decoding apparatus may decode the context syntax elements for thecurrent subblock included in the residual information based on thespecific number and, more specifically, may decode the different contextsyntax elements based on the specific number according to whether atransform skip is applied to the current block. For example, when thetransform skip is applied to the current block, the decoding apparatusmay decode preset context syntax elements, for example, sig_coeff_flag,coeff_sign_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gtx_flag, based on a context model until the specific numberfor the transform coefficients arrives. (S1920). Subsequently, thedecoding apparatus may decode remaining transform coefficients based ona bypass model (S1930).

For example, when the transform skip is applied to the current block,the decoding apparatus may decode the context syntax elements of atransform coefficient for the current subblock of the current blockbased on context. The context syntax elements may include a significantcoefficient flag indicating whether the transform coefficient is anon-zero transform coefficient, a sign flag indicating the sign of thetransform coefficient, a first transform coefficient level flagindicating whether the level of the transform coefficient is greaterthan a first threshold, a parity level flag indicating the parity of thetransform coefficient level of the transform coefficient, and a secondtransform coefficient level flag indicating whether the transformcoefficient level of the transform coefficient is greater than a secondthreshold. The significant coefficient flag may be sig_coeff_flag, thesign flag may be coeff_sign_flag, the first transform coefficient levelflag may be abs_level_gt1_flag or abs_level_gtx_flag, the parity levelflag may be par_level_flag, and the second transform coefficient levelflag may be abs_level_gt3_flag or abs_level_gtx_flag. For example, whenthe second transform coefficient level flag is expressed asabs_level_gtx_flag, the flag may be encoded according to a certainiteration statement, and thus the second transform coefficient levelflag is not a single value but may be a third transform coefficientlevel, a fourth transform coefficient level, a fifth transformcoefficient level, or the like, which is different from the secondtransform coefficient level.

Alternatively, when the transform skip is not applied to the currentblock, the decoding apparatus may decode the context syntax elements ofa transform coefficient for the current subblock of the current blockbased on context.

For example, the context syntax elements may include a significantcoefficient flag indicating whether the transform coefficient is anon-zero transform coefficients, a first transform coefficient levelflag indicating whether the level of the transform coefficient isgreater than a first threshold, a parity level flag indicating theparity of the transform coefficient level of the transform coefficient,and a second transform coefficient level flag indicating whether thetransform coefficient level of the transform coefficient is greater thana second threshold. The first transform coefficient level flag may beabs_level_gt1_flag or abs_level_gtx_flag, the parity level flag may bepar_level_flag, and the second transform coefficient level flag may beabs_level_gt3_flag or abs_level_gtx_flag. For example, when the secondtransform coefficient level flag is expressed as abs_level_gtx_flag, theflag may be encoded according to a certain iteration statement, and thusthe second transform coefficient level flag is not a single value butmay be a third transform coefficient level, a fourth transformcoefficient level, a fifth transform coefficient level, or the like,which is different from the second transform coefficient level.

Specifically, when the total number of context-coded bins of contextsyntax elements for transform coefficients preceding a transformcoefficient in the scan order among the transform coefficients for thecurrent subblock reaches the specific number (i.e., is the specificnumber or greater), signaling of context syntax elements for thetransform coefficient may be omitted (i.e., the context syntax elementsfor the transform coefficient may not be signaled), a bypass syntaxelement that is bypass-coded for the transform coefficient may bedecoded, and the value of the transform coefficient may be derived basedon the decoded bypass syntax element. That is, the value of thetransform coefficient may be derived based on the bypass syntax elementthat is bypass-coded.

For example, when the total number of context-coded bins for contextsyntax elements of transform coefficient 0 to transform coefficient n ofthe current subblock reaches the specific number, signaling of contextsyntax elements for transform coefficient n+1 of the current subblockmay be omitted, and a bypass syntax element for the n+1th transformcoefficient included in the residual information may be decoded. Thatis, the value of transform coefficient n+1 may be decoded based on thevalue of the bypass syntax element.

That is, for example, when the transform skip is applied to the currentblock, if the total number of context-coded bins for significantcoefficient flags, sign flags, first transform coefficient level flags,parity level flags, and second transform coefficient level flags fortransform coefficient 0 to transform coefficient n determined by thescan order among the transform coefficients for the current subblockreaches the specific number (i.e., is the specific number or greater),signaling of a significant coefficient flag, a sign flag, a firsttransform coefficient level flag, a parity level flag, and a secondtransform coefficient level flag for transform coefficient n+1determined by the scan order may be omitted, a bypass syntax elementthat is bypass-coded for quantized transform coefficient n+1 may bedecoded, and the value of quantized transform coefficient n+1 may bederived based on the value of the bypass syntax element. Here, thebypass syntax element may include abs_remainder of the absolute value ofthe remainder of a transform coefficient level coded at a predeterminedscanning position.

In summary, in decoding the transform coefficients, the abs_remainder ofthe absolute value of the remainder of the transform coefficient levelmay refer to (1) a remaining value after coding, such as significantcoefficient flags, sign flags, first transform coefficient level flags,parity level flags, a second transform coefficient level flag, a thirdtransform coefficient level, and a fifth transform coefficient level,according to a level value when the total number of context-coded binsdoes not reach the specific number, or (2) the absolute value of anactual transform coefficient when the total number of context-coded binsreaches the specific number.

Alternatively, for example, when the transform skip is not applied tothe current block, if the total number of context-coded bins forsignificant coefficient flags, first transform coefficient level flags,parity level flags, and second transform coefficient level flags fortransform coefficient 0 to transform coefficient n determined by thescan order among the transform coefficients for the current subblockreaches the specific number (i.e., is the specific number or greater),signaling of a significant coefficient flag, a first transformcoefficient level flag, a parity level flag, and a second transformcoefficient level flag for transform coefficient n+1 determined by thescan order may be omitted, a bypass syntax element that is bypass-codedfor quantized transform coefficient n+1 may be decoded, and the value ofquantized transform coefficient n+1 may be derived based on the value ofthe bypass syntax element. Here, the bypass syntax element may includeabs_remainder of the absolute value of the remainder of a transformcoefficient level coded at a predetermined scanning position anddec_abs_level indicating an intermediate value coded with a Golomb-Ricecode at a scanning position.

The decoding apparatus derives transform coefficients for the currentsubblock based on the decoded context syntax elements and bypass syntaxelements (S1940).

The decoding apparatus may derive the transform coefficients based onthe entropy-decoded context syntax elements for the transformcoefficient. The residual information may also include a sign flagindicating the sign of the transform coefficient. The decoding apparatusmay derive the sign of the transform coefficient based on the sign flag.A syntax element indicating the sign flag may be coeff_sign_flag. Forexample, the decoding apparatus may derive the transform coefficientbased on the value of the transform coefficient and the sign.

The decoding apparatus derives residual samples for the current blockbased on the transform coefficients (S1950). For example, the decodingapparatus may derive the residual samples for the current block based onthe transform coefficients. That is, the decoding apparatus may deriveresidual samples for the current subblock in the current block based onthe transform coefficients.

For example, when the value of the transform skip flag for the currentblock is 1, the decoding apparatus may derive the residual samples forthe current block based on the transform coefficients. For example, whenthe value of the transform skip flag for the current block is 1, thedecoding apparatus may derive the residual samples for the current blockby dequantizing the transform coefficients.

Alternatively, when the value of the transform skip flag for the currentblock is 1, the decoding apparatus may rearrange the transformcoefficients and may derive the rearranged transform coefficients as theresidual samples for the current block. For example, the decodingapparatus may rearrange the transform coefficients using variousrearrangement methods. That is, the decoding apparatus may transfer thetransform coefficients from a derived position to a different positionthrough various rearrangement methods.

In one example, the decoding apparatus may rearrange the transformcoefficients through a rearrangement method of 180-degree rotation.Specifically, for example, the decoding apparatus may rearrange thetransform coefficients of the current block to symmetrical positionswith respect to the center of the current block.

Alternatively, in one example, the decoding apparatus may rearrange thetransform coefficients through a rearrangement method of antidiagonalmirroring. Specifically, for example, the decoding apparatus mayrearrange the transform coefficients to symmetrical positions withrespect to a right upward diagonal of the current block. Here, the rightupward diagonal may refer to a right upward diagonal passing through thecenter of the current block.

Alternatively, in one example, the decoding apparatus may rearrange thetransform coefficients through a rearrangement method of main diagonalmirroring. Specifically, for example, the decoding apparatus mayrearrange the transform coefficients to symmetrical positions withrespect to the left upward diagonal of the current block. Here, the leftupward diagonal may refer to a left upward diagonal passing through thecenter of the current block.

Alternatively, in one example, the decoding apparatus may rearrange thetransform coefficients through a rearrangement method of verticalflipping. Specifically, for example, the decoding apparatus mayrearrange the transform coefficients of the current block to symmetricalpositions with respect to a vertical axis of the current block. Here,the vertical axis may be a vertical line passing through the center ofthe current block.

Alternatively, in one example, the decoding apparatus may rearrange thetransform coefficients through a rearrangement method of horizontalflipping. The decoding apparatus may rearrange the transformcoefficients of the current block to symmetrical positions with respectto a horizontal axis of the current block. Here, the horizontal axis maybe a horizontal line passing through the center of the current block.

Alternatively, in one example, the decoding apparatus may rearrange thetransform coefficients through a method of deriving separate layersbased on the distance to a reference sample of the current block andrearranging the layers according to an inverse raster order.

For example, the decoding apparatus may set layers for the current blockbased on distances from reference samples of the current block. Here,the reference samples may include top reference samples and leftreference samples of the current block. For example, when the size ofthe current block is N×N and an x component of the position of atop-left sample position of the current block is 0 and the y componentthereof is 0, the left reference samples may be p[−1][0] to p[−1][2N−1],and the top reference samples may be p[0][−1] to p[2N−1][−1]. When thesize of the current block is N×N, the layers may include a first layerto an Nth layer. The Nth layer may be the last layer, and N may be equalto the width or the height of the current block. For example, the firstlayer may include positions from which the distance to the nearestreference sample is 1, a second layer may include positions having fromwhich the distance to the nearest reference sample is 2, and the Nthlayer may include positions from which the distance to the nearestreference sample is N.

Subsequently, the decoding apparatus may scan the transform coefficientsin the inverse raster order. That is, the decoding apparatus may scanthe transform coefficients of the current block from right to left andfrom bottom to top. Next, the decoding apparatus may rearrange thetransform coefficients in the layers in the scan order. Here, thetransform coefficients may be rearranged in an order from the firstlayer to the Nth layer. The transform coefficients may be rearrangedbased on a transverse-first scan or a longitudinal-first scan in therearranged layers.

For example, the transform coefficients may be preferentially rearrangedfrom right to left at lateral positions of the top-left position of therearranged layers, and when there are longitudinal positions of thetop-left position of the rearranged layers, the transform coefficientsmay be rearranged from top to bottom at the longitudinal positions ofthe top-left position of the rearranged layers after being arranged atthe lateral positions. Alternatively, for example, the transformcoefficients may be preferentially rearranged from top to bottom atlongitudinal positions of the top-left position of the rearrangedlayers, and when there are lateral positions of the top-left position ofthe rearranged layers, the transform coefficients may be rearranged fromleft to right at the lateral positions of the top-left position of therearranged layers after being arranged at the longitudinal positions.

Alternatively, in one example, the decoding apparatus may rearrange thetransform coefficients through a method of deriving separate layersbased on a distance to a reference sample of the current block andrearranging the layers according to a diagonal scan order.

For example, the decoding apparatus may set layers for the current blockbased on distances from reference samples of the current block. Here,the reference samples may include top reference samples and leftreference samples of the current block. For example, when the size ofthe current block is N×N and an x component of the position of atop-left sample position of the current block is 0 and the y componentthereof is 0, the left reference samples may be p[−1][0] to p[−1][2N−1],and the top reference samples may be p[0][−1] to p[2N−1][−1]. When thesize of the current block is N×N, the layers may include a first layerto an Nth layer. The Nth layer may be the last layer, and N may be equalto the width or the height of the current block. For example, the firstlayer may include positions from which the distance to the nearestreference sample is 1, a second layer may include positions having fromwhich the distance to the nearest reference sample is 2, and the Nthlayer may include positions from which the distance to the nearestreference sample is N.

Subsequently, the decoding apparatus may scan the transform coefficientsin the diagonal scan order. That is, the decoding apparatus may scan thetransform coefficients of the current block from top right to bottomleft and from bottom right to top left. Next, the decoding apparatus mayrearrange the transform coefficients in the layers in the scan order.Here, the transform coefficients may be rearranged in an order from thefirst layer to the Nth layer. The transform coefficients may berearranged based on a transverse-first scan or a longitudinal-first scanin the rearranged layers.

For example, the transform coefficients may be preferentially rearrangedfrom right to left at lateral positions of the top-left position of therearranged layers, and when there are longitudinal positions of thetop-left position of the rearranged layers, the transform coefficientsmay be rearranged from top to bottom at the longitudinal positions ofthe top-left position of the rearranged layers after being arranged atthe lateral positions. Alternatively, for example, the transformcoefficients may be preferentially rearranged from top to bottom atlongitudinal positions of the top-left position of the rearrangedlayers, and when there are lateral positions of the top-left position ofthe rearranged layers, the transform coefficients may be rearranged fromleft to right at the lateral positions of the top-left position of therearranged layers after being arranged at the longitudinal positions.

Alternatively, for example, the decoding apparatus may set layers forthe current block based on distances from top reference samples of thecurrent block. For example, when the size of the current block is N×Nand an x component of the position of a top-left sample position of thecurrent block is 0 and the y component thereof is 0, the top referencesamples may be p[0][−1] to p[2N−1][−1]. When the size of the currentblock is N×N, the layers may include a first layer to an Nth layer. TheNth layer may be the last layer, and N may be equal to the width or theheight of the current block. For example, the first layer may includepositions from which the distance to the nearest top reference sample is1, a second layer may include positions having from which the distanceto the nearest top reference sample is 2, and the Nth layer may includepositions from which the distance to the nearest top reference sample isN. That is, the first layer may be a first row of the current block, thesecond layer may be a second row of the current block, and the Nth layermay be an Nth row of the current block.

Subsequently, the decoding apparatus may scan the transform coefficientsin the diagonal scan order. That is, the decoding apparatus may scan thetransform coefficients of the current block from top right to bottomleft and from bottom right to top left. Next, the decoding apparatus mayrearrange the transform coefficients in the layers in the scan order.Here, the transform coefficients may be rearranged in an order from thefirst layer to the Nth layer. Rearrangement of the transformcoefficients may be performed in the order from the first layer to theNth layer, and the transform coefficients may be rearranged based fromright to left at the positions of the rearranged layers.

Alternatively, for example, the decoding apparatus may set layers forthe current block based on distances from left reference samples of thecurrent block. For example, when the size of the current block is N×Nand an x component of the position of a top-left sample position of thecurrent block is 0 and the y component thereof is 0, the left referencesamples may be p[−1][0] to p[−1][2N−1]. When the size of the currentblock is N×N, the layers may include a first layer to an Nth layer. TheNth layer may be the last layer, and N may be equal to the width or theheight of the current block. For example, the first layer may includepositions from which the distance to the nearest left reference sampleis 1, a second layer may include positions having from which thedistance to the nearest left reference sample is 2, and the Nth layermay include positions from which the distance to the nearest leftreference sample is N. That is, the first layer may be a first column ofthe current block, the second layer may be a second column of thecurrent block, and the Nth layer may be an Nth column of the currentblock.

Subsequently, the decoding apparatus may scan the transform coefficientsin the diagonal scan order. That is, the decoding apparatus may scan thetransform coefficients of the current block from top right to bottomleft and from bottom right to top left. Next, the decoding apparatus mayrearrange the transform coefficients in the layers in the scan order.Here, the transform coefficients may be rearranged in an order from thefirst layer to the Nth layer.

Rearrangement of the transform coefficients may be performed in theorder from the first layer to the Nth layer, and the transformcoefficients may be rearranged based from top to bottom at the positionsof the rearranged layers.

The decoding apparatus may determine whether to rearrange the transformcoefficients based on various conditions. Alternatively, the decodingapparatus may derive a rearrangement method applied to the transformcoefficients based on various conditions.

For example, the decoding apparatus may receive the transform skip flagfor the current block and may determine whether to rearrange thetransform coefficients based on the transform skip flag. The transformskip flag may indicate whether the transform is applied to the transformcoefficients. For example, when the value of the transform skip flag is1, it may be determined to rearrange the transform coefficients. Thatis, when the value of the transform skip flag is 1, the decodingapparatus may rearrange the transform coefficients. When the value ofthe transform skip flag is 0, it may be determined not to rearrange thetransform coefficients. That is, when the value of the transform skipflag is 0, the decoding apparatus may derive the residual samples forthe current block based on the transform coefficients rather thanrearranging the transform coefficients.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on the number of samples of thecurrent block. For example, when the number of samples of the currentblock is less than a specific value, it may be determined to rearrangethe transform coefficients. That is, when the number of samples of thecurrent block is smaller than the specific value, the decoding apparatusmay rearrange the transform coefficients. When the number of samples ofthe current block is the specific value or greater, it may be determinednot to rearrange the transform coefficients. That is, when the number ofsamples of the current block is the specific value or greater, thedecoding apparatus may derive the residual samples for the current blockbased on the transform coefficients rather than rearranging thetransform coefficients. The specific value may be 64.

Alternatively, for example, when the number of samples of the currentblock is less than 64, the decoding apparatus may rearrange thetransform coefficients through the rearrangement method of 180-degreerotation. When the number of samples of the current block is 64 orgreater, the decoding apparatus may not rearrange the transformcoefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on the number of samplesof the current block.

For example, when the number of samples of the current block is lessthan 64, the decoding apparatus may rearrange the transform coefficientsthrough the rearrangement method of 180-degree rotation, and when thenumber of samples of the current block is 64 or greater, the decodingapparatus may rearrange the transform coefficients through therearrangement method of mirroring. Alternatively, in another example,when the number of samples of the current block is less than 64, thedecoding apparatus may rearrange the transform coefficients through oneof the rearrangement methods described above, and when the number ofsamples of the current block is 64 or greater, the decoding apparatusmay not rearrange the transform coefficients.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on the shape of the current block.For example, when the current block is a square block, it may bedetermined to rearrange the transform coefficients. That is, when thecurrent block is a square block, the decoding apparatus may rearrangethe transform coefficients. When the current block is a non-squareblock, it may be determined not to rearrange the transform coefficients.That is, when the current block is a non-square block, the decodingapparatus may derive the residual samples for the current block based onthe transform coefficients rather than rearranging the transformcoefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on the shape of thecurrent block. For example, when the current block is a square block,the decoding apparatus may rearrange the transform coefficients throughthe rearrangement method of mirroring, and when the current block is anon-square block, the decoding apparatus may rearrange the transformcoefficients through the rearrangement method of 180-degree rotation.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on the ratio of the width of thecurrent block to the height thereof. For example, when the ratio of thewidth of the current block to the height is 2 or greater or is ½ or less(i.e., when a value obtained by dividing the width of the current blockby the height is 2 or greater or is ½ or less), the decoding apparatusmay rearrange the transform coefficients through the rearrangementmethod of mirroring, and when the ratio of the width of the currentblock to the height is less than 2 and is greater than ½ (i.e., thevalue obtained by dividing the width of the current block by the heightis less than 2 and is greater than ½), the decoding apparatus may derivethe residual samples for the current block based on the transformcoefficients rather than rearranging the transform coefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on the ratio of the widthof the current block to the height thereof. For example, when the ratioof the width of the current block to the height is 2 or greater or is ½or less (i.e., when a value obtained by dividing the width of thecurrent block by the height is 2 or greater or is ½ or less), thedecoding apparatus may rearrange the transform coefficients through therearrangement method of mirroring, and when the ratio of the width ofthe current block to the height is less than 2 and is greater than ½(i.e., the value obtained by dividing the width of the current block bythe height is less than 2 and is greater than ½), the decoding apparatusmay rearrange the transform coefficients through the rearrangementmethod of 180-degree rotation.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on an intra prediction mode for thecurrent block. For example, when the prediction direction of the intraprediction mode for the current block is a horizontal direction or theintra prediction mode for the current block is an intra prediction modein which prediction is performed mainly using a left reference sample,the decoding apparatus may rearrange the transform coefficients throughthe rearrangement method vertical flipping, and in other cases, thedecoding apparatus may derive the residual samples for the current blockbased on the transform coefficients rather than rearranging thetransform coefficients. Alternatively, for example, when the predictiondirection of the intra prediction mode for the current block is avertical direction or the intra prediction mode for the current block isan intra prediction mode in which prediction is performed mainly using atop reference sample, the decoding apparatus may rearrange the transformcoefficients through the rearrangement method vertical flipping, and inother cases, the decoding apparatus may derive the residual samples forthe current block based on the transform coefficients rather thanrearranging the transform coefficients.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on an intra predictionmode for the current block. For example, when the prediction directionof the intra prediction mode for the current block is a horizontaldirection or the intra prediction mode for the current block is an intraprediction mode in which prediction is performed mainly using a leftreference sample, the decoding apparatus may rearrange the transformcoefficients through the rearrangement method vertical flipping, andwhen the prediction direction of the intra prediction mode for thecurrent block is a vertical direction or the intra prediction mode forthe current block is an intra prediction mode in which prediction isperformed mainly using a top reference sample, the decoding apparatusmay rearrange the transform coefficients through the rearrangementmethod vertical flipping.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on a flag indicating whether torearrange the transform coefficients, which is received through ahigh-level syntax. For example, the decoding apparatus may receive theflag indicating whether to rearrange the transform coefficients througha sequence parameter set (SPS) or a picture parameter set (PPS) and maydetermine whether to rearrange the transform coefficients based on theflag.

Alternatively, in another example, a rearrangement method for thetransform coefficients may be determined based on information indicatingthe rearrangement method for the transform coefficients, which isreceived through a high-level syntax. For example, the decodingapparatus may receive the information indicating the rearrangementmethod for the transform coefficients through a sequence parameter set(SPS) or a picture parameter set (PPS) and may determine whether torearrange the transform coefficients based on the information.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on a prediction mode for thecurrent block. For example, when the prediction mode for the currentblock is intra prediction, it may be determined to rearrange thetransform coefficients. That is, when the prediction mode for thecurrent block is intra prediction, the decoding apparatus may rearrangethe transform coefficients. When the prediction mode for the currentblock is inter prediction, it may be determined not to rearrange thetransform coefficients. That is, when the prediction mode for thecurrent block is inter prediction, the decoding apparatus may derive theresidual samples for the current block based on the transformcoefficients rather than rearranging the transform coefficients.

Alternatively, in another example, whether to rearrange the transformcoefficients may be determined based on whether the transformcoefficients are quantized. For example, when quantization has beenapplied to the transform coefficients, it may be determined to rearrangethe transform coefficients. That is, when quantization has been appliedto the transform coefficients, the decoding apparatus may rearrange thetransform coefficients. When no quantization has been applied to thetransform coefficients, it may be determined not to rearrange thetransform coefficients. That is, when no quantization has been appliedto the transform coefficients, the decoding apparatus may derive theresidual samples for the current block based on the transformcoefficients rather than rearranging the transform coefficients.

Alternatively, for example, when the value of the transform skip flagfor the current block is 0, the decoding apparatus may derive theresidual samples for the current block by inversely transforming thetransform coefficients. Alternatively, for example, when the value ofthe transform skip flag for the current block is 0, the decodingapparatus may dequantize the transform coefficients and may inverselytransform the dequantized transform coefficients, thereby deriving theresidual samples for the current block.

The decoding apparatus may generate a reconstructed picture based on theresidual samples (S1960). For example, the decoding apparatus may derivea prediction sample by performing an inter prediction mode or an intraprediction mode on the current block based on the prediction informationreceived through the bitstream and may generate the reconstructedpicture by adding the prediction sample and the residual sample. Forexample, the prediction information may include information indicatingan intra prediction mode for the current block. Alternatively, theprediction information may include motion information on the currentblock.

Subsequently, as described above, if necessary, an in-loop filteringprocedure, such as deblocking filtering, SAO, and/or ALF procedures, maybe applied to the reconstructed picture in order to improvesubjective/objective image quantity.

FIG. 20 schematically illustrates a decoding apparatus that performs animage decoding method according to the present disclosure. The methodillustrated in FIG. 19 may be performed by the decoding apparatusillustrated in FIG. 20. Specifically, for example, an entropy decoder ofthe decoding apparatus of FIG. 20 may perform S1900 to S1930 of FIG. 19,a residual rearranger of the decoding apparatus of FIG. 20 may performS1940 and S1950 of FIG. 19, and an adder of the decoding apparatus ofFIG. 20 may perform S1960 of FIG. 19. Further, although not shown, aprocess of obtaining the prediction information on the current blockthrough the bitstream may be performed by the entropy decoder of thedecoding apparatus of FIG. 20, and a process of deriving the predictionsample for the current block based on the prediction information may beperformed by a predictor of the decoding apparatus of FIG. 20.

According to the foregoing present disclosure, it is possible toincrease the efficiency of residual coding.

Further, according to the present disclosure, the total number ofcontext-coded bins for context syntax elements for transformcoefficients in a current block, which is included in residualinformation, may be limited to a predetermined specific number or less,thereby reducing data coded based on context.

In addition, according to the present disclosure, the number ofcontext-coded bins for a current subblock may be adjusted consideringthe total number of context-coded bins for context syntax elementsrather than considering coding of each context syntax element, thusreducing the complexity of residual coding and improving overall codingefficiency.

In the foregoing embodiments, although the methods are explained basedon flowcharts including a series of steps or blocks, the presentdisclosure is not limited to the order of steps, and a certain step maybe performed in order or step different from that described above or maybe performed concurrently with another step. Further, it may beunderstood by a person having ordinary skill in the art that steps shownin a flowchart are not exclusive and that another step may beincorporated or one or more steps of the flowchart may be removedwithout departing from the scope of the present disclosure.

The embodiments illustrated in the present disclosure may be embodiedand performed on a processor, a microprocessor, a controller, or a chip.For example, functional units shown in each drawing may be embodied andperformed on a computer, a processor, a microprocessor, a controller, ora chip. In this case, information for implementation (e.g., informationon instructions) or algorithms may be stored in a digital storagemedium.

Further, a decoding apparatus and an encoding apparatus to which theembodiments of the present disclosure are applied, may be included in amultimedia broadcasting transceiver, a mobile communication terminal, ahome cinema video device, a digital cinema video device, a surveillancecamera, a video chat device, a real time communication device such asvideo communication, a mobile streaming device, a storage medium, acamcorder, a video-on-demand (VoD) service providing device, anover-the-top (OTT) video device, an Internet streaming service providingdevice, a three-dimensional (3D) video device, a video telephony videodevice, a transportation terminal (e.g., an in-vehicle terminal, anairplane terminal, a vessel terminal, or the like), and a medical videodevice, and may be used to process a video signal or a data signal. Forexample, the over-the-top (OTT) video device may include a game console,a Blu-ray player, an Internet access TV, a Home theater system, asmartphone, a Tablet PC, a digital video recorder (DVR) and the like.

In addition, a processing method to which the embodiments of the presentdisclosure are applied may be produced in the form of a program executedby a computer, and be stored in a computer-readable recording medium.Multimedia data having a data structure according to the presentdisclosure may also be stored in a computer-readable recording medium.The computer-readable recording medium includes all kinds of storagedevices and distributed storage devices in which computer-readable dataare stored. The computer-readable recording medium may include, forexample, a Blu-ray Disc (BD), a universal serial bus (USB), a ROM, aPROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppydisk, and an optical data storage device. Further, the computer-readablerecording medium includes media embodied in the form of a carrier wave(e.g., transmission over the Internet). In addition, a bitstreamgenerated by the encoding method may be stored in a computer-readablerecording medium or transmitted through a wired or wirelesscommunication network.

Additionally, the embodiments of the present disclosure may be embodiedas a computer program product by program codes, and the program codesmay be executed on a computer by the embodiments of the presentdisclosure. The program codes may be stored on a computer-readablecarrier.

FIG. 21 illustrates the structure of a content streaming system to whichthe embodiments of the present disclosure are applied.

The content streaming system to which the embodiments of the presentdisclosure are applied may generally include an encoding server, astreaming server, a web server, a media storage, a user equipment, and amultimedia input device.

The encoding server functions to compress to digital data the contentsinput from the multimedia input devices, such as the smart phone, thecamera, the camcorder and the like, to generate a bitstream, and totransmit it to the streaming server. As another example, in a case wherethe multimedia input device, such as, the smart phone, the camera, thecamcorder or the like, directly generates a bitstream, the encodingserver may be omitted.

The bitstream may be generated by an encoding method or a bitstreamgeneration method to which the embodiments of the present disclosure areapplied, and the streaming server may temporarily store the bitstreamwhile transmitting or receiving the bitstream.

The streaming server transmits multimedia data to the user equipment onthe basis of a user's request through the web server, which functions asan instrument that informs a user of what service there is. When theuser requests a service which the user wants, the web server transfersthe request to the streaming server, and the streaming server transmitsmultimedia data to the user. In this regard, the content streamingsystem may include a separate control server, and in this case, thecontrol server functions to control commands/responses betweenrespective equipments in the content streaming system.

The streaming server may receive contents from the media storage and/orthe encoding server. For example, in a case the contents are receivedfrom the encoding server, the contents may be received in real time. Inthis case, the streaming server may store the bitstream for apredetermined period of time to provide the streaming service smoothly.

Examples of the user equipment may include a mobile phone, a smartphone,a laptop computer, a digital broadcasting terminal, a personal digitalassistant (PDA), a portable multimedia player (PMP), a navigationsystem, a slate PC, a tablet PC, an ultrabook, a wearable device (e.g.,a watch-type terminal (smartwatch), a glass-type terminal (smartglasses), and a head-mounted display (HMD)), a digital TV, a desktopcomputer, a digital signage, or the like. Each server in the contentstreaming system may be operated as a distributed server, in which casedata received by each server may be processed in a distributed manner.

1-11. (canceled)
 12. An image decoding method performed by a decodingapparatus, the method comprising: receiving a bitstream comprisingresidual information; deriving transform coefficients for a currentblock based on the residual information; deriving residual samples forthe current block based on the transform coefficients; and generating areconstructed picture based on the residual samples for the currentblock; wherein the deriving of the transform coefficients comprises:determining a maximum value for a number of context-coded bins forcontext syntax elements for the current block; decoding the contextsyntax elements for the current block comprised in the residualinformation based on the maximum value; deriving transform coefficientsfor the current block based on the decoded context syntax elements;wherein, based on a transform skip being applied to the current block, asignificant coefficient flag relating to whether a transform coefficientis a non-zero transform coefficient, a sign flag relating to a sign ofthe transform coefficient, a first transform coefficient level flagrelating to whether a transform coefficient level is greater than afirst threshold, a parity level flag relating to a parity of thetransform coefficient level of the transform coefficient, and a secondtransform coefficient level flag relating to whether the transformcoefficient level of the transform coefficient is greater than a secondthreshold are decoded based on a context model until the maximum valueis reached, and wherein, when a total number of context-coded bins forcontext syntax elements of transform coefficient 0 to transformcoefficient n of the current block reaches the maximum value, a bypasssyntax element for transform coefficient n+1 comprised in the residualinformation is decoded.
 13. The image decoding method of claim 12,wherein the maximum value is set based on a size of the current block.14. The image decoding method of claim 12, wherein a value of transformcoefficient n+1 is derived based on a value of the decoded bypass syntaxelement.
 15. The image decoding method of claim 12, wherein the bypasssyntax element comprises abs_remainder for a remaining absolute value ofa transform coefficient level coded at a predetermined scanningposition.
 16. An image encoding method performed by an encodingapparatus, the method comprising: deriving residual samples for acurrent block; deriving transform coefficients in the current blockbased on the residual samples; and encoding residual informationcomprising information on the transform coefficients, wherein theencoding of the residual information comprises: deriving a maximum valuefor a number of context-coded bins for context syntax elements for thecurrent block; encoding the context syntax elements based on the maximumvalue; and generating a bitstream comprising residual information on thecurrent block comprising the encoded context syntax elements, wherein,based on a transform skip being applied to the current block, asignificant coefficient flag relating to whether a transform coefficientis a non-zero transform coefficient, a sign flag relating to a sign ofthe transform coefficient, a first transform coefficient level flagrelating to whether a transform coefficient level is greater than afirst threshold, a parity level flag relating to a parity of thetransform coefficient level of the transform coefficient, and a secondtransform coefficient level flag relating to whether the transformcoefficient level of the transform coefficient is greater than a secondthreshold are encoded based on a context model until the maximum valueis reached, and wherein, when a total number of context-coded bins forcontext syntax elements of transform coefficient 0 to transformcoefficient n of the current block reaches the maximum value, a bypasssyntax element for transform coefficient n+1 comprised in the residualinformation is encoded.
 17. The image encoding method of claim 16,wherein the maximum value is set based on a size of the current block.18. The image encoding method of claim 16, wherein a value of transformcoefficient n+1 is derived based on a value of the encoded bypass syntaxelement.
 19. The image encoding method of claim 16, wherein the bypasssyntax element comprises abs_remainder for a remaining absolute value ofa transform coefficient level coded at a predetermined scanningposition.
 20. A non-transitory computer-readable digital storage mediumthat stores a bitstream comprising residual information generated by amethod, the method comprising: deriving residual samples for a currentblock; deriving transform coefficients in the current block based on theresidual samples; and encoding residual information comprisinginformation on the transform coefficients, wherein the encoding of theresidual information comprises: determining a maximum value for a numberof context-coded bins for context syntax elements for the current block;encoding the context syntax elements based on the maximum value; andgenerating the bitstream comprising the residual information on thecurrent block comprising the encoded context syntax elements, wherein,based on a transform skip being applied to the current block, asignificant coefficient flag relating to whether a transform coefficientis a non-zero transform coefficient, a sign flag relating to a sign ofthe transform coefficient, a first transform coefficient level flagrelating to whether a transform coefficient level is greater than afirst threshold, a parity level flag relating to a parity of thetransform coefficient level of the transform coefficient, and a secondtransform coefficient level flag relating to whether the transformcoefficient level of the transform coefficient is greater than a secondthreshold are encoded based on a context model until the maximum valueis reached, and wherein, when a total number of context-coded bins forcontext syntax elements of transform coefficient 0 to transformcoefficient n of the current block reaches the maximum value, bypasssyntax element for transform coefficient n+1 comprised in the residualinformation is encode.